Just Build
The NewPipe App can be built using Android Studio. For more in-depth install guide use Google.
Once you have installed Android Studio, either fork the repo (main repo) if you want to submit your changes as a pull-request later and then clone your fork, or if you just want to read the source, clone the main repo. Once it's done downloading, go ahead and open it with Android Studio. You can now run it over adb 
, or build a dev-signed apk. If you get stuck, don't be afraid to take the opportunity to learn some Google-fu, and if you are truly stuck, ask for help on Stack Overflow or from one of the contributors.
Install Your Build
The project is set up in such a way that the debug APK you build will have a custom package name based on your git branch name. This means that you can safely install your build on your test device without affecting the release build at all.
Fix A Problem!
Please read the CONTRIBUTING Guidelines before you start your next fix/awesome feature!