turn Unknown Sources on
device settings/security/ Unknown sources
Download F-droid
From browner go to https://f-droid.org/ F-Droid
Dowload the package
Install
Once downloaded and installed, F-Droid will check your device for compatibility with the apps in its market. The compatibility check can take a few minutes to complete.
I’ve done this, but also installed APKUpdater from apkmirror. This is good to help you stay up to date with the latest versions of apps that you might not be downloading from F-Droid.
After apk’s install, F-Droid will update repos and upgrade itself. If it stays on a blank page, swip back to launch update… and wait a minute (notification shows process). Prefer wifi for that.
Then, F-Droid will update repos when launched. You can choose the way (data’s, WiFi) in Settings (back, right) > Download and Updates…