From D&DWiki's SRD
How Combat Works
Combat is cyclical; everybody acts in turn in a regular cycle of rounds. Combat follows this sequence:
- Each combatant starts out flat-footed. Once a combatant acts, he or she is no longer flat-footed.
- Determine which characters are aware of their opponents at the start of the battle. If some but not all of the combatants are aware of their opponents, a surprise round happens before regular rounds of combat begin. The combatants who are aware of the opponents can act in the surprise round, so they roll for initiative. In initiative order (highest to lowest), combatants who started the battle aware of their opponents each take one action (either a standard action or a move action) during the surprise round. Combatants who were unaware do not get to act in the surprise round. If no one or everyone starts the battle aware, there is no surprise round.
- Combatants who have not yet rolled initiative do so. All combatants are now ready to begin their first regular round of combat.
- Combatants act in initiative order (highest to lowest).
- When everyone has had a turn, the combatant with the highest initiative acts again, and steps 4 and 5 repeat until combat ends.
The Combat Round
Each round represents 6 seconds in the game world. A round presents an opportunity for each character involved in a combat situation to take an action.
Each round’s activity begins with the character with the highest initiative result and then proceeds, in order, from there. Each round of a combat uses the same initiative order. When a character’s turn comes up in the initiative sequence, that character performs his entire round’s worth of actions. (For exceptions, see Attacks of Opportunity and Special Initiative Actions.)
For almost all purposes, there is no relevance to the end of a round or the beginning of a round. A round can be a segment of game time starting with the first character to act and ending with the last, but it usually means a span of time from one round to the same initiative count in the next round. Effects that last a certain number of rounds end just before the same initiative count that they began on.