How to Bind Block States with Inventory Contents

The vanilla example I'm gonna use is a brewing stand. The block state changes based on what's in the inventory. I know I'll need to use procedures, but it's important to note I'm entirely new to them (so pictures would be most helpful) and I have like, no coding experience.

I don't need it to be so complex that each inventory position is tied to a different block state (like how with a brewing stand, if you move potions around it changes the block state. That's not necessary. The only important part is how many items are in the inventory).

Thank you in advance, I appreciate any help I can get on this