Nick here from Shopify.
It's difficult to figure out exactly why this might be happening without taking a look at your admin. There are a couple of reason which spring to mind about why this could be. Just to make sure that the collections are being made available as per the help guide here. Also just to double-check and make sure your products are available for the online store as seen in the screenshot below:
Regarding your domain question. Can I ask where you purchased the domain from? Was it from Shopify or a third party domain host? Once you purchase a domain, you need to then add it to your store, and that might be what's happening here. You can see the guide Shopify has for adding a domain here.
All the best, Nick