Source Core Rulebook pg. 637 2.0
A creature called by a spell or effect gains the summoned trait. A summoned creature can't summon other creatures, create things of value, or cast spells that require a cost. It has the minion trait. If it tries to Cast a Spell of equal or higher level than the spell that summoned it, it overpowers the summoning magic, causing its own spell to fail and the summon spell to end. Otherwise, the summoned creature uses the standard abilities for a creature of its kind. It generally attacks your enemies to the best of its ability. If you can communicate with it, you can attempt to command it, but the GM determines the degree to which it follows your commands.

Immediately when you finish Casting the Spell, the summoned creature uses its 2 actions for that turn. A spawn or other creature generated from a summoned creature returns to its unaltered state (usually a corpse in the case of spawn) once the summoned creature is gone. If it's unclear what this state would be, the GM decides. Summoned creatures can be banished by various spells and effects. They are automatically banished if reduced to 0 Hit Points or if the spell that called them ends.