In Android studio, this can be done from the Quickstart panel. Just choose "Configure", then "SDK Manager". In the SDK Tools tab of the SDK Manager, make sure that "Android Support Repository" is installed, and that the latest "Android SDK build-tools" are installed. Click "OK" to return to the Quickstart panel. You may also need to install API version 28 in the SDK platforms tab.
1. Open Android Studio. On a new installation, the Quickstart panel will appear. If you have open projects, close them using "File > Close Project" to see the Quickstart panel.
2. From the Quickstart panel, choose "Checkout from Version Control" then "git".
Code contributions should be sent via Github as pull requests, from feature branches [as explained here](https://help.github.com/articles/using-pull-requests).