Meter and locations are typically paired and will remain a pair before, during, and after a customer has moved in. They only considered part of a trinity when assigned to a customer.
Locations are the physical locations where customers connect. Meters will be connect to locations thru the manage location screen, which is the default view for a location.
To access the manage location screen click on 'Loc/Meters' in the top menu. Then search for the 'Location ID'. Once you see the location you're working with click on the 'Loc ID'.
Notice control defaults to the install meter screen. Once the meter is added several more options will be available. Click on Add Meter
The first section will search for unassigned meters. Left to right, the columns are for the meter serial number, communication type, form factor, voltage per phase, current per phase, and unit of measure. The meter serial numbers are clickable for meter selection.