Can someone explane how Disengageing form combat works?

disengaging is simply a manuever. (be it your free one, one you spend 2 strain on, or one generated from the dice pool).

when you disengage, you move from engaged to short range.

disengagement isn't necessarily ONLY from melee or brawling combat. it could be disengaging from an ally or cover too.

note: you do not need to disengage from ranged combat.