Hi and welcome!
As you said you're new, let me say this:
1) This new feature is applied at product level (can be different for EACH of your producs).
2) In RTD there's normally only one "store", which is the container of all your products.
3) There's the possibility of creating multiple stores, and each of them can have specific products included.
This to quickly say that allowing only user uploads is a matter of a specific product, but has nothing to do with stores.
"Stores" are just basically the containers of styles, icons and text labels. In other terms, stores allows you to control the look, not the features.
So, all you have to do is create the products you need, with the feature enabled/disabled as needed.
If you need the same product but offering both "full cliparts" and "user uploads only" versions, you'll need to create 2 copies of that product, and change
Enable Custom Cliparts ONLY accordingly.
What your users will see depends on which produict they'll be visiting. Each product has a link, and there are many ways to manage them.
You could use RTD catalog, but you could also link directly the specific product's designer straight from your website.
For new RTD user there may be some misunderstanding in terminology, that's why I thought to post this quick thing about products and stores. I hope I was clear enough!
If not, feel free to stress your sales rep with no mercy or... reply here again telling us what's still "obscure" so that we can go in better detail. 2nd choice preferred!
