Running a game using the beginner box, The cleric/wizard can use Spellcraft once per day to examine a magic item. And although not part of the beginner box rules, Appraise can be used to determine the value of any item.
Do PC's automatically know everything there is to know about a non-magical item they find? for example if they find a special (non-magic) weapon, do they get to know the stats and features straight away? or is there some mechanic to learning about the weapon?
Things like this are up to the DM, really. It also depends on the world you're playing in. In a world where everyone has been fighting with muskets for hundreds of years, finding a bow might be puzzling to the characters. But generally, common items are common because they are found everywhere and everyone knows about them. In a 'generic' fantasy world it seems reasonable that any adventurer would recognize a sword or an axe, even if it has some kind of unique design.
As for common weapon stats, it doesn't really matter that players know them. It doesn't mean that their characters know how to use those weapons, after all.
I don't really know what you mean by 'special non-magic weapons'. In case of things like a whip or a spiked chain it's still pretty obvious what you can do with it, even if the characters don't know how. I know that a whip can be used to trip people, even though I have no idea how i would have to handle the weapon.
If it's some kind of unique weapon that's not in the standard game, decide as you wish. You can often just describe the item, and see what the players come up with. If they really have no idea and you think that they should know at least something, you can always go with something like 'the bard in your party realizes that he has seen this weapon being wielded by a king's bodyguard years ago in his travels far away.'
TLDR; For common items, it generally doesn't matter much that the players know all about it.
