For this achievement, you have to play as the Medic class.
To revive a player, walk over an unconcious friendly player and press Y. You should take out a device and zap him back to conciousness.
To supply a health pack, simply hit the Y button when your health pack charge displays at least a "1".
To use the healing aura, you must first buy it from the class menu. It is available for $500 for basic use. To use it, hit up on the d-pad.