Dropshipping in summary: you find products you want to sell, import them and increase the price. You list them on your Shopify store and start marketing. When a customer buys the product you pay the original cost to the supplier and they ship it directly to them, you keep the markup as your profit!
That was short but hope enough to give you an idea of dropshipping. Here's a more in-depth FAQ that will hopefully answer follow-up questions you might have.
Hope this helps and if you have other questions please ask! We are here to help!