I'm confused I thought in christianity you were not supposed to summon spirits, why do some churches summon?

The Holy Spirit is not some guy being brought back to the dead, nor calling on demons or any other kind of summoning. The Holy Spirit is the third part of the trinity, kind of like how we're Mind Body Soul. And as for using the word 'summon' I don't know what you mean by that. I've never heard of a church holding a seance for God.