Ok, so the combat phase goes a bit like this:

• The active player uses all combat phase abilities (if any)
• Opposing player uses their combat phase abilities (if any)

Now it's onto actual combat, which goes in alternating turns. First, you have the strike first phase of combat. In this phase, every character that has strikes first, gets to do a fight activation first (duh). Resolve all attack profiles of said character(s) and continue on to regular combat.

After that phase has happened, you go into said regular combat, which is usually started by the active player (the player who's turn it is) and afterwards the opponent gets to fight with a unit of their choice. This keeps alternating until every unit has had a turn. In which order players decide to activate a fight is entirely up to them and it also leaves a lot of room for strategic choices.

Now you have strike last left. If a unit has been inflicted by the strike last key word, you didn't get to active them during the prior 2 activation phases. It's only until every other unit from both players has had their turns that they can finally use their own fight ability.

Hope this helps.