First of all give us details of your computer. Laptop or desktop, OS, version of Resolve, GPU and it's driver, and amount of ram, etc. The more information the better.
Have you actually loaded video clips into the Media Pool? If you click on the Media Pool tab to open it, does it contain any clips?
If the question is rather a "how do I do it" one, This should help you.
https://www.blackmagicdesign.com/uk/products/davinciresolve/trainingAn example of the Media Pool tab open in the Edit page.
Single Screen Media Pool.jpg