"Add friend" is available at the top of the user's profile. And, if you are logged in as an Administrator, the User Manager in the Administration Panel is where you go to make a user an Admin. (With the same rights as you... so be careful!)
you edit the user, and you will see a spot that says something along the lines of "Is User an Administrator" and set it to yes / true.
You should be able to add friends by going to user profile. Can you please explain bit more of your problem about what second URL?
Yes you can add as many administrators as you can.