My character is Dragonborn, and has a breath weapon. Making a breath weapon attack is a standard action. I am wondering if I can make a breath weapon and also make one attack with my weapon?
I know that you can make a move action and a standard action in a combat. If one can normally make one attack, then move 30ft, why couldn't one simply not move and make one melee attack?
Not normally. As Colin explained, attacking and using a breath weapon are both standard actions. You can't normally take two standard actions in a round, and you can't substitute a move action for a standard action.
You can however take the Metabreath Feat Quicken Breath (Draconomicon). That lets you use your breath attack as a free action, which would let you do both in one round. Using it adds +4 to the number of rounds you have to wait before using your breath weapon again.
Alternately, if you have an way to gain additional standard actions (like from the Factotum class), you could use that additional action to let you both breathe and attack.
A move action simply does not take as long as a standard action. You can turn a standard action into a move action, simply giving up however much extra time the standard action would have taken, but you cannot do the reverse because it would take more time.
How much time is explicitly left undefined. The whole round is roughly six seconds, with everyone acting near-simultaneously (in-character, people are not waiting their turn), but no further breakdown is given aside from Standard > Move > Swift > Free > Non. Note you cannot trade a standard or a move action for a swift the way you can with standard to move, however. For that one, the reason is just “because the rules say so” and because a lot of things are balanced by there only being one swift action per round.
So you cannot choose to not move (trading in your move action) in order to attack (a standard action) or use a breath weapon (also a standard action). Note that most spells are a standard action; a wizard getting a pair of spells per round just because he hasn’t moved would be insane, and even more overpowered than the wizard already is.
No.
Making a swing with your weapon is normally a standard action. Using your breath weapon is a standard action. On your turn you can take a standard action + move action. However, the move action cannot be converted into a standard action.
One thing that is necessary to understand is, that the difference between move actions and standart actions differs not only in the time spent (which is explicitly undefined, as Kryan mentioned), but also in the effort invested. If we were to look at it from a simulationist point of view, moving 20 ft and attacking in the same round might be viable, but using a breath weapon and recovering from it fast enough to still be able to perform a series of attacks (a single attack roll) might be harder.
Also, this is a balancing element, as mentioned, and simply solves a lot of stuff within the games bounds. Therefore, be wary of changing it, it probably will lead to widespread confusing uber-combos.
