Here is a viedo that shows an overhead squat: https://www.muscleandstrength.com/exercise
However, if you are completely unfamiliar with freeweights, I don't think I'd jump in with an overhead squat first thing. I'm not a trainer or anything, but that seems like a rather advanced lift. I'd start with air squats and make sure my form was correct, then move to squatting the bar, checking form, then to adding weights.
If your gym doesn't have a squat rack, I'm not sure what I'd sub with. You could do regular squats with the bar, but you couldn't go very heavy because you'd still have to get the bar over your head on to your shoulders without infury. Perhaps dumbbell squats. You could also use dumbbells to do overhead suqats, I would imagine, if you're set on doing overhead squats.
Edited by: JENMC14 at: 1/10/2013 (15:34)