Install F-Droid from the official site (should be an APK - it's safe), and, from within F-Droid, you can install Neo Store. Then you can use Neo Store to access F-Droid stuff. Just make sure you stick to official/trusted repos, and you should be fine. I mainly use the Play Store for stuff, but sometimes the updates drop faster on F-Droid (or there's a handful of FOSS apps that aren't in the Play Store).