depends on type, on a 737-300, on the first press of the TOGA you get reduced go around thrust if the auto throttle is armed, on second push you get full go around thrust as determined by FMC.
IF you are doing a single channel approach, the autopilot disengages, the flight director commands the track the a/c was following when TOGA pushed and commands a pitch up, can't remember what attitude it goes to , as you raise the flaps it pitches down to command the speed for the next flap setting. On a dual channel approach(autoland) the autopilot stays engaged and flies the go around.
if no FD selected it pops up when you press TOGA and dissapears at, I think, 2000ft? radio alt. you then need to select other modes such as level change for pitch and maybe heading select for roll. please correct me if some of this is wrong.