I'm assuming you're referring to the Frontier Airlines terminal at Hartsfield-Jackson Atlanta International Airport (ATL). Frontier Airlines operates out of Terminal N at ATL.
Terminal N at ATL is located on the north side of the airport, near the Georgia International Convention Center. It is a small terminal with limited facilities, as Frontier Airlines is currently the only airline operating out of this terminal.
If you're arriving at ATL and need to find the Frontier Airlines terminal, you can follow the signs for Terminal N or ask for directions from airport staff. If you're departing from ATL on Frontier Airlines, you should check in at the Frontier Airlines ticket counter in Terminal N.