If the property is a new lot, you need to record it with Orange County Land Records. Orange County will assign a Property Identification Number (a PIN). When Carrboro Planning receives the PINs from Orange County, addresses are assigned for the properties and an address assignment letter goes out to the property owners, the post office, utilities, government entities, and 911. That letter creates the address and gets it into the 911 system.
If the property already exists and has a PIN, but has no address or has an address that is not in the 911 system, in which case you may have trouble getting cable or power or water hookup or the post office won't deliver your mail, you need to contact the Carrboro Planning Department (919-918-7328) to get an address assigned.