Okay, open the front door. The A-pillar is the part of the frame that runs diagonally up each side of the windshield to the roof.
Open the front door and the rear door. The B-pillar is the part of the frame that runs vertically between the doors, up to the roof and down to the floor.
Open the rear door. The C-pillar is the part of the frame that runs diagonally up each side of the rear window, up to the roof.
