Scroll down till you see assets and a list of links. You'll want one of the Android apks, but tbh I'm not sure which, as it depends on your device. In my case (and maybe yours), it was the first link, e.g. liftoff-v0.9.13-arm64v8a-android.apk.
After downloading it should prompt you to open the download, and on doing so it will probably ask for permission to install unknown apps or apps from non-Play Store sources (such as your browser). Give it the okay and it should begin installing.
If you're a little concerned about leaving that permission open, go into settings and search, "Install unknown apps" and scroll down to your browser (which should show itself as set to allow or the like after doing this), tap that and it will display another screen where you can disallow installing apps from it.