I am creating a spell based on the move that a Xorn can do. However, I want it to be able to use a spell slot when casted, instead of at will. How do I do that?

You make it a spell with a level instead of making it a Cantrip. “At Will” basically just means the same basic Spellcasting as Cantrips. What are you trying to recreate, Earth Glide?

I tried changing the Level on it but it just shows as a level 1 or 2 spell that can be cast at will. And yes I am recreating earth glide. 

In the homebrew spell generator? How are you giving it to the character?

I've created this piece of armor for him to wear that give him the ability to cast a few spells. So I've created Earth Glide in the Homebrew spell Creator and then added the spell to the armor

Are you trying to make it so that the item grants the spell knowledge to the PC and they would spend their own spell slots to cast it? Because that won’t work. You have to either set it in the armor how many times/day they can cast it, or you have to set a charge cost and then give the armor charges.

Okay i wasnt sure if i had to make it use charges. Thank you.

No problem. Either charges or uses/day.