To sign up for CBS All Access, just follow these steps:

On your Android device

1. Open the CBS app. 
2. From the Menu, tap “Subscribe”.
3. Select Commercial Free.
4. Enter your information to sign up for a CBS account. If you already have an existing CBS.com account, simply select "Already have an account? Sign In".
5. Confirm your subscription on the next screen by tapping "Subscribe". You may be prompted toenter your Google Play password. 
6. After the confirmation screen appears, you can start streaming CBS All Access!