This guide describes basic steps of the Android development environment setup that are required to run React Native android apps on an android emulator. We don't discuss developer tool configuration such as IDEs here.
Genymotion is much easier to set up than stock Google emulators. However, it's only free for personal use. If you want to use the stock Google emulator, see below.
1. Start a new shell and run `android`; in the window that appears make sure you check:
* Intel x86 Atom System Image (for Android 5.1.1 - API 22)
* Intel x86 Emulator Accelerator (HAXM installer)
2. Click "Install Packages".
3. [Configure hardware acceleration (HAXM)](http://developer.android.com/tools/devices/emulator.html#vm-mac), otherwise the emulator is going to be slow.