Q: Add a new user

I have Macbook 2008.

I just got it as a present ... it was not mine originally.

My name is A

Under /Users I see only name of user B (original owner) but not A

I could login into system as A but I can restart computer only as user B

When I'm in Users & Groups I see name A and it has admin privilages.

My question:

how could I add A to /Users?

how could I make A being able to restart computer as well?

Thanks