How to do android beta testing

I am new to android developing. I have just finished building my first app, which I want to publish in the play store. But, before that I want to test it using the android's open beta testing service. I read android's developer material, also went through some of the questions already asked here. But, I didn't get info what I am looking for.

Please help me with the following..

1. To beta test, should I upload the APK in the debug version or the release version?
2. If it is a release version, how can I generate a signed APK?