This is a frequently asked question and I am sure by opening the link given below all of your questions will be answered. For accessing this feature of adding users, you should be the Admin in your Team account.
Hope this helps
You currently have an individual membership so cannot add an additional user to this. The 2nd user can sign up for their own individual account using their Adobe ID or you could switch to a Teams account with 2 seats if that suits your needs better.