How can I assign custom shipping rates to my products?

Guys, I’m tearing my hair out here… please help.

I am unable to assign custom shipping rates to any of my products.

I have created custom profiles as per instruction yet when I go in to add a product it says “Your store doesn’t have any products yet.” but my store does have products - they are all showing in the general shipping rates section and I can’t seem to move them.

It is driving me crazy, surely it can’t be this difficult to assign custom shipping rates to different items?!