These apps aren't on Google Play — they're APKs hosted on GitHub Releases. Here's how to get one running on your phone.
Sideloaded apps don't come from Google Play, so your browser needs permission to install them. When you download an APK, your browser or Android will prompt you to allow installs from that source — accept it. You'll only need to do this once per app.
Once the download finishes, open it from your notification shade, or from your Files app's Downloads folder.
Android will likely warn you that the app wasn't scanned or isn't from the Play Store. That's expected for sideloaded apps — tap "Install anyway" to continue.
Updates are manual — there is no auto-update for sideloaded apps. Come back to trApps and re-download when a new version is posted; the app will show an "Update" badge once you have an older version installed.