On your PlayStation 4:

1. Open the CBS All Access app.
2. Select "Sign up for CBS All Access". 
3. You'll be directed to a screen with an activation code. Make of note of your code - you'll need it for the next step.
3. Using a web browser on your computer or mobile device, go to www.cbs.com/xboxone and enter the activation code.  
4. From there, you'll be prompted to create a CBS All Access account. 
5. Choose the Commercial Free plan, enter your payment information, and click "Start CBS All Access".
6. You'll see a confirmation screen on your web browser, and your PS4 screen will refresh. 

You can now start streaming CBS All Access on your PS4!