Using the Japan Rail Passin Tokyo

Hello,

I'm not very sure of how to use the JR Pass within Tokyo. I understand it's not valid for metro lines, but only for the JR operating lines but I can't seem to find any information regarding the actual use, meaning
- does it have to be validated like an ordinary ticket? - is it enough to have it with you alongside your ID card? - do you have to go to a ticket office in order to get an actual ticket (free of charge)?

Hope you can help me out!

Thank you very much :)