Thread:Maxus1576/@comment-16107481-20141202183128/@comment-7341673-20141202183949

They're esentially Trap Monsters (in a sense) in that you set them in the Trigger Zone (face-down) and when their Trigger Condition is met, their effect activates (the effect that comes after the "Trigger Condition:" text). Some of them Special Summon themselves (a Trigger Summon) or just have effects that activate (or have both). Once they activate and resolve, if they don't summon themselves, they go to the Graveyard.

That's the basic gist of it.