Don't give me credit for this information. This was posted by someone else last year, and I copied and saved it. It worked fine last year (the first year I took MARTA instead of renting a car). Thanks to whomever wrote it in the first place.
Steve in Philly
PP Marta
1) go to Ground Transportation area of the airport
2) locate the MARTA station via signs
3) purchase a token at window or vending machine
4) stick token in token slot, and go through gate
5) go up escalator to the trains (both will be going north, since the airport is the southernmost station)
6) get off at N5, Arts Center
then, if the same thing happens to you that happens to me every single year:
7) exit station through wrong door, get all turned around, and walk in a huge circle to find the venue/hotels,
And you don't really have to worry about getting on the wrong train. The airport is the southern most station. So they will all be going North and just look for the Arts Center Station like the last guy said. It's always very clear what station you are at and there are maps and things on the train that will tell you what the next stations are.
...and to make the search a bit easier ( i know we didn't had a clue two years back) , take the station exit on the left side of the building (left is when looking in driving direction)...