need help with UI

I am trying to make a UI that has a sort of modular system where if you hit a button it opens up a new UI. I have that part working. the issue is that I can't make the UI that was opened craft anything. all the tutorials I see online link the UI to a block and it works, but no one seems to have a tutorial on a UI that ISN'T linked with a block that crafts items. I have tried replacing all the of that block with the parts that just say at the entity

I have no idea how to make a crafting UI that is apart from an in world block