Havoc Jester's ability triggers when you sacrifice it. If you sacrifice other permanents at the same time, it triggers for them as well.

If you sacrifice a permanent as part of casting a spell or activating an ability, Havoc Jester's ability will resolve before that spell or ability.

Havoc Jester's ability is a triggered ability, not an activated ability. It doesn't allow you to sacrifice a permanent whenever you want; rather, you need some other way of sacrificing permanents.

A legendary permanent that is put into a graveyard because of the “legend rule” isn't sacrificed.