Most installations will have meters and locations paired. If that's the case the only thing needed to make a trinity is create a new customer and assign them a paired location and meter. If the customer is already in the system and just needs a new location to be assigned, the same steps can be used.
Since the registration process will vary by installation, the focus will be on assigning an existing customer to a paired Location and Meter.
From the account screen click on 'Add Location'. You may notice this option is also available from the Control tab as 'Move IN'.
Under the Control tab follow the on screen instructions and click Move IN when done.