I believe most if not all Trailblazers have 5 seats. But, please, don't get a car like that for your first car. Besides the fact that it's a terrible car, a first car should be cheap and small, like a Honda Civic, Toyota Corolla, or Subaru Impreza.
They all have at least 5 seats 2 front captain's/bucket seats, rear is a 60/40 split bench that can seat 3 people. The EXT model has a third row that will sit 2 more people , usually that seat is used for kids because it has very little leg room. You can tell the EXT model from the standard models (LS, LT, LTZ) it looks more bubbled in the back than the others and are a few inches longer.