Outside of combat, things will be free-form (as this is an RP), and I'll process all actions that require feats taken in the order they were given to me. Otherwise, feel free to talk and act with little consequence. Just remember that too much noise and loitering may attract zombies.
In combat, things will be a little more structured.
A round is the time it takes for each player and NPC to have one turn. The fastest players will be able to enact feats/attacks first in combat situations.
During each player and NPC's turn, they may either do two feats (example: moving, reloading, surveying their surroundings, setting a trap), or one feat and one attack.
Turn order will be determined at the beginning of battle and at the beginning of each round, and generally won't change unless an event, injury, or item changes a character or NPC's speed. All ties are given to the enemy. The only exception is that any character that initiates combat will always go first.
Example 1: Player A, B, and C have Slow, Average, and Slow speeds respectively, and are fighting a single, basic zombie (slow). That means the round order will go A, B, Zombie, and C unless the first three are injure in a way to slow them down.
Example 2: Using the same stats as the first example, C initiates combat. The first round's order will be C, A, B, Zombie, and unless there are any slowing injuries, the rest of the rounds will continue with A, B, Zombie, and C.