The user management is a server side feature, meaning all the profiles are saved on the server portion of Mediaportal 2 and then distributed through all the clients where the User Management Feature is enabled.
Note: At the moment only watched status is maintained between different clients installations. User settings are stored per seat, which means every user can have different settings (and different skin) per different seats.
To configure and enable User Management you first have to attach to the home server.
Then navigate to Settings -> Users.
From there you'll have the option to configure the following features: