I do, however, see 'import UIKit' or 'import Foundation.' This makes it look like you need to import built-in modules, but not the modules you create in separate files.

If you click the "+" button in Swift Playgrounds you'll see three options. The first is snippets, the second is images. Among the image options you can upload photos that you have already. With an uploaded image, click on the image and it will put it on a line in your Playground.