Here’s a quick summary of the steps involved.
And here’s a fairly detailed, step-by-step, click-by-click breakdown of each process.
You need to have an 'approved', 'published' Facebook Store (on a Facebook Business Page) which is usually approved in 48 hours after setup) before you can be approved for the Instagram Channel.
Having an FB store is good. But it's empty until you create a catalog for it, and then fill that catalog with products.
The correct FB Store must connect to the correct IG account.
Finally, enable product tagging on your Instagram account.
Well, if everything went smoothly, you’re done.
Now you just need to create a standard Instagram photo-post.
When it comes time to ‘tag’ it normally, now TWO options will appear.
Tag people or tag products?
Make your choice and have fun!