You can't miss it - from the main train station is a direct connection to the IAA - also from the Airport - the trains are running continously during show days/hours. The show area is about 20 big halls with cars and equipment.
Lots of fun and exitment. I would recommend to get a pass during Industry Days (two days before the show opens to the public), then you can really see something - otherwise you have to fight your way through the crowds to get closer to the cars.