Alignment is Hard
People have deeply ingrained ideas about what alignment is, and it varies wildly from table to table (and from edition to edition). I've always liked the foreword explanation in the Alignment section of the 3.5e PHB - unlike nearly any other explanation, I felt it clearly identified and made very clear this basic rule;
Alignment is the means by which you go about your goals, not your goals themselves.
Except for certain characters (Paladins, Blackguards, and Outsiders) for whom their alignment is their purpose for existence, your alignment is meant to represent your outlook on the world, the rose-coloured glasses you wear rather than your actual eyeballs. A Chaotic Evil character has goals, and those goals might be the same as a Lawful Good character - it's how he goes about those goals that makes him Chaotic and Evil, not necessarily the goals themselves.
As such, a group of people with the same Alignment can be very, very different. But let's look at what makes Chaotic and Evil, well, Chaotic and Evil.
'Butterfly lemon pies!'
Chaotic characters or individuals are that tiny segment of the population that departs from Neutral (baseline) in the extent that they are able to adapt and roll with punches. When the plan goes off the rails, plows into a snowbank, and explodes, they thrive. Often they are seen by groups as 'stupid' or unintelligent, but if anything, the opposite is true - to thrive in chaos, you have to be able to analyze situations and come to workable solutions really really fast.
A good rule of thumb is that Chaotic characters are the kind of character who works and takes advantage of an existing situation, and a Lawful character is one who will try to change a situation to his or her preference. You can totally have a Lawful character whose modus operandi is to cause riots and wreak havoc - if that is his preferred environment, and he tries to create it whenever possible to achieve his goals.
If you think of a James Bond style character, a secret agent who goes into situations dressed in the right clothes, with a walther ppk, the right lie and split-second decisionmaking processes, that's a Chaotic character. Really, a 'fluid, evolving plan' is another way of saying 'Chaos'.
A chaotic character is an opportunist. They can have plans, but they drop them the first time they think of or see something better. They're always on the lookout for the next big thing, they play fast and loose, and often pick the short-term gain over the long one. Overall (on the larger stage of Nations and City-States), Chaotic tends to have short-term wins but ultimately be out-maneuvered by the long-range planning of Lawful.
Examples of Chaotic societies/groups; Mongols (Highly organized but very fluid in that organization and chain of command), later Roman empire (capable individuals promoted and given power, only way to maintain control of such a large area with poor communications), insurgency groups and intelligence agencies (rely on capable individuals taking advantage of opportunities).
Lawful societies/groups; modern corporations (corporate monoculture), modern bureaucracies (standardization over success), most of the Chinese Imperial periods (structure and form over capability), Banks throughout history.
'Kill them all, but make the children watch.'
Good and Evil are in some ways more straightforward than Chaotic and Lawful, but in other ways harder. People have very strong ideas and opinions about what Good and Evil are, but a lot of those ideas are societal or religious or philosophical and differ from person to person - much less what the hell an Umber Hulk thinks about utilitarian consequentialism vs catholic original sin.
Evil is about a complete lack of empathy.
When it comes down to it, empathy, caring about others by likening them to you, is the sole determining factor for the vast majority of humanity's morality - and it's the best starting point for defining Evil that you're probably going to find.
Now - people or monsters or devils or whatever might be sadistic, or might think that ripping people's toenails off is hilariously funny, or it's an important part of their culture, or whatever. I'm not going to talk about that. That might make them Detect as Evil, and it's probably much more common on the deeper end of the Alignment pool, but that comes under Goals, which is not what i'm discussing - i'm discussing Alignment.
When someone is Evil, they are going to go about their goals in an Evil manner. Which means, according to my view of it, they are going to get what they want in the absolute most callous way. Generally, even Neutral villains will try, perhaps not greatly, but at least a little, to mitigate suffering. When it costs them nothing, they'll let the prisoner have water. They'll not shoot the bystander during the Bank Robbery - they'll push them aside instead.
The Evil Character does not care. Why did they shoot that child? Because it was more amusing than not shooting the child. Why did they kill that hostage that was in the way? Marginally faster than pushing them out of the way. Wounded hostages slow police down more than unwounded ones - dead kidnappees can't tell the police details about their kidnapper. Someone cuts you off in traffic? Taping a pipe bomb to their exhaust pipe is a slight bit of satisfaction - worth ten times the effort.
Often without thinking about it, human beings (and other empathic creatures) try to limit or reduce the suffering of others they empathize with. Evil, simply doesn't. If someone can't do something for you, hurting or killing them gives you something you want, and no-one is going to get you for hurting or killing them, there's no compunction to stop the murder occurring - even if the reason is 'because I like murdering' or 'to get his candybar'.
Evil, as I view it, is simply psychopathy. There can be Evil characters who gain nothing or lose things by murder or violence, or any of the other traditional 'hallmarks of evil' and so just... don't do it. They can be lauded as the good and great in a society that isn't a weird faerunian 'society of murderers and bandits' (Zhentil Keep?), just because the rewards for not doing murder outweigh the reasons the character has to murder.
That said, when you have no empathy, there's little chance you're not screwing over others in some way. Competitive advantage is a real thing, and those with no compunctions about doing anything at all to gain it usually have bodies of some kind in the basement.
The Mongols were a semi-nomadic tribal structure based around the protection of a clan's warriors. If a slave of a clan was killed by a warrior of another clan, or a woman, or whatever, that clan sought redress, and if it wasn't met, there'd be a duel or an outright clan war.
That is a good example of an 'Evil' society, but it's scarcely the only one.
The Byzantines had an active class of nobles and a chaotic system of government based around backstabbing and betrayal. Empathy was an actively bad thing to have in the high tiers of their society, and turnover was high - ergo, the top tiers of their government were probably usually Evil (although crusading reformers play well with the mob and gain enough XP by going against the odds to take over periodically).
The problem though, is that there is no Human society that is Usually Evil. Most Humans are, by the alignment system, Neutral. Even giant jerks like the Assyrians are mostly passing fads. That said though, understanding an entire nation of psychopaths is not impossible, you just have to understand that on the whole, Empathy is good for nations.
So you can have Orcs that care about their families, or people they like (friends), but you can't have orcs that care about strangers or people they dislike. They'll screw those people over, and that's that - and in their society, that won't be weird.
But ultimately, what occurs in a society is largely a result of how that society keeps order, how it polices it's citizenry, how resources are kept safe from thieves, etc. Whether a Warlord rules with an iron fist (think of an african military dictatorship - crude rules enforced more with an eye to keeping people down than to fairness and justice), whether the orcs exist in Clans of individuals (by creed or by blood or by tradition) who band together for protection from other clans and enforce cooperation by means of brutal execution or torture or expulsion of clan members who break the rules without sufficient clout to get away with it, whether they have a highly stratified society where sometimes it's fine to murder people and other times if you do you get jailed and executed, all of these things will inform on orc society, or if it's a band of orcs, the society from which they come.
Notably, Orcs have negatives to the mental stats compared to humans - they will be less well organized, waste more time and effort with regular tasks, and get along less well amongst each other, so that will also inform their group actions.
But ultimately any society has to function to exist - it has to produce enough food to feed the populace, enough goods to trade, enough children to replace the deaths. The challenge is inventing a society which works with the Chaotic nature of Orcs, the Evil nature of Orcs, and the Stupid nature of Orcs, and still functions and exists - or at least seems enough like it might to fool your audience.
LotR and Warhammer solve this by making Orcs be born from the ground and eat anything. In DnD you don't normally have this option, so you need to actually sit down and think, about everything from ecology to foreign relations, to create a realistic set of Orcs for your world and setting.
A good example of a Chaotic character problem-solving.
Evil is about solving problems through other people's suffering, not suffering for it's own sake.