First, download and launch the CBS app. Then:
1. From the menu, select Settings > Subscribe.
2. Select subscription plan (either Commercial Free or Limited Commercials).
3. Select "Using your Google account". (If you don't have a CBS.com account and/or a Google Play account, select "Using your email" and follow the instructions.)
5. Select "Subscribe".
That's it! Now you can start streaming CBS All Access.