There are two types of apps.
Steps for importing an msapp.
1. Go to https://us.create.powerapps.com/studio/# (see the link below) – you should get redirected to https://eu.create.powerapps.com/studio/# if in Europe
2. Download one of the apps below. The app MUST be of a type *.msapp for this technique to work
3. Go back to the site above
4. Click Open
5. Browse for your file
6. Open it.
7. Nearly there
8. Make sure that you save the app (so that it lives on the web)
Steps for downloading a *.zip file