Exit the gate are in Terminal A and follow the signs to Concourses C and D. There's a waiting area there where the mobile lounges dock (think of the lounge as a large bus).

There will either be a lounge docked at the terminal (the entrance doors will be open) or the doors will be closed and there will be a countdown clock indicating when the next one will depart. In that case, you hang out in the waiting area until a lounge docks.

Wait for the lounge to Concourse C. While C and D are both part of one long concourse, in general, you are not going to save any time catching a D lounge for a C departure gate.

The lounge will drive you from A to C, it's a neat drive as you have to cross the tarmac and will see many planes at the gates and moving on the tarmac.