Hank here from Shopify.
Great question, when it comes to adding products to your store, the most common issue to the one you described is product visibility. Adding products to your sales channels is very important as this is how your customers see your products through the likes of your website and social media pages. Can you confirm that your collections are available on your chosen sales channels? The below is from my test store, so you should see something similar in your store.
Another common issue can be if the products are set for future publishing. This is when you have uploaded products to your store, but you don't want them going live until X date.
Lastly, depending on the theme you are using, can be another reason as to why you do not see the collections. Within your admin, navigate to Online Store > Themes > Customize, which will bring you to the theme editor. Within the editor, you can add collections to your theme by adding a section and selecting "featured products" or "featured collection".
Can you try the above suggestions to see if this resolves the issue for you? Let me know how you get on!
All the best,