how do i know if my terraain is AWD

From what I have found they are either front wheel drive or all wheel drive. Look under your vehicle. If you have a drive shaft going from the front (transmission) all the way back to the rear axle then yours will be an AWD model. These models will also have cv type axles going to each of the front wheels. The front wheel drive models will only have the axles going to the front wheels and not have the drive shaft going to the rear axle.

an easier way is to look at the back tailgate- an AWD will have the letters in chrome stating AWD on the bottom right corner of the tailgate. I hope this helps

You cannot tell by casual observation beneath the GMC Terrain if it is 2WD or 4WD. The drive shafts may be apparent when on a hoist - but you cannot see anything from just bending down on a knee and looking underneath. I know this because we just tried it with our rental.