Hi
Everyone (human) can initiate ONE attack per round. Everyone can 'react' to EVERY attack made against them (if they are conscious) - however, after one 'reaction' the Outnumbering rule is applied if further attacks are made on that same human character.
Outnumbering - humans are outnumbered after 'reacting' once in a round. A ghoul with 3 attacks, is outnumbered after 'reacting' 3 times in a round. And so on.
Initiating - attacking (melee), attempting a maneuver, shooting (firearm, bow) or throwing (knife etc.) - or do one thing else (cast a spell, move away, use a non-combat skill, etc.). You make or take one significant action that you initiate.
Reacting - dodge, fightback (melee), or maneuver. If being shot at - you may dive for cover (dodge) or stand and take it (hope they miss). You may react to all attacks directed at you.
Everyone initiates their action on DEX in a round.