The NPCs are driven by the Action Table - see the Turn Sequence section on page 16. The Action Table determines when they can shoot or perform other actions.
Under the Shooting Section, also page 16, there's a good subsection about Cover and its use.
Thanks for the answer (and excuse me as english is not my first language) in the turn sequence it doesnt tell anything about NPCs
• Consult the Action Table (page 58).
• Roll 1d6 to see who has the Advantage.
• Score a 1, 2 or 3 and you do.
• Score a 4, 5, or 6 and they do.
• Note that mounted Characters facing unmounted
Characters will increase their chance of winning
the Advantage by one.
• Modify the Rep of each Leader by any applicable
Attribute.
• Each Leader now rolls 2d6 versus its modified Rep.
• Determine how many d6 are passed. This determines
which side is Active and what each Character can do.
• After the Active side has finished all of its actions,
both sides take the Will to Fight Test (page 59).
• After the Will to Fight Test is taken, if there are any
figures left on the Battle Board, the Inactive side
becomes Active and can carry out its actions.
• After the newly Active side has finished all of its
actions, both sides take the Will to Fight Test.
• Repeat the process until only one or no sides remain
on the Battle Board. Yes, both sides could decide to
leave the Battle Board at the same time!
And the Action Table says, indeed, when can the characters shoot, but my question is, is there an order of what actions makes the NPCs?
Action table, possible actions, when could an NPC charge?:
• Shoot.
• Charge into Melee.
• Recover from Duck Back.
• Mount up or dismount.
• Leave the Battle Board.
Thanks for all the kind answers!