How to install apps from F-Droid

Open f-droid.org on your Android phone and download the F-Droid client. Check that the address is really f-droid.org before you download anything.

Open the downloaded file. Android will ask you to allow installs from your browser. Allow it for this install, then turn the permission off again in settings if you prefer.

Open F-Droid and let it refresh its app list. Search for an app and tap Install. F-Droid builds apps from their published source code, and it updates them for you too.