2. You will get a warning similar to this one, click 'Ok'
3. Click 'Open' once it's done Downloading
4. You will get a warning again if you haven't previously installed an APK manually, click on 'Settings'
5. Flip the switch to on by clicking on it
6. You will be asked to install this app, click Install. The process is the same as on the App Store from that point forward.