Giving another use admin access?
 

I put the user in the same usergroup as me, but they can't access the whole Admin CP.

How do I fix this?

You need to edit their access to quite a bit of the admin functions. Just putting them in the "Admin" usergroup doesn't do this.

once you put a member into the admin group...it will ask you to edit administrator permissions.

Then you can choose what they can do or cant do.

(If I was you...I'd make sure that you're set up as a super-administrator in your config file, just incase)