Welcome to the Shopify community!
and Thanks for your question.
Please share your site URL,
So I will check and provide a solution here.
Nick here from Shopify.
From what you've written it sounds like you need to add the products to your collection. There are two different types of collections (manual and automatic, once you know which one you have created you can add products to it then. Shopify also has a YouTube tutorial as in introduction to collections that you might find useful.
Regarding adding images under featured collection, is this in your store admin under Online store > Themes?
Let me know if you have any other questions about this!
All the best, Nick