Thank you for the answer @alizain !
To build on that answer, Shopify provides you with the essential tools to create and launch your online business; however, we do not have a hand in your day-to-day affairs which would include product sourcing. The products you sell would be managed by you as the business owner.
You're welcome to sell your own product if you have a product line to sell. Alternatively, if you do not have a product on hand, then you can consider what @alizain suggested, along with print on demand. The difference between the two is that Print on Demand would allow you to place your own design/content onto products, whereas dropshipping allows you to sell already created products. Both dropshipping and print on demand allow you to select products from a supplier, resell the product at an increased cost while leaving the shipping and fulfillment process up to the supplier. Freeing up time for you to focus more on sales, the design of your website, and customer service.
For print on demand, there are a number of apps you can choose from that offer a wide variety of products. You can view print-on-demand apps here. We offer free courses on print on demand here.
If you're unsure of what to sell, then you could review what products are currently trending through our blog post here.
Let me know if you have any other questions!