Before you graduate to barbell squats, you should be able to goblet squat to parallel using a dumbbell or kettlebell for 25 unbroken reps. It's a test of relative strength, which means it'll show you whether or not you're strong for your size.
Grab a kettlebell or dumbbell that's 50% of your bodyweight.
Squat it for 25 reps.
A male weighing 200 pounds would complete 25 reps of goblet squats using a 100-pound dumbbell without any half-reps or pauses. To pass this test, the 25 reps must be unbroken and at parallel depth.
If you can pass this relative strength test, get the bar on your back. If you can't, work on your movement quality, bring up your weak links and then do a barbell squatting. Of course you could also be too fat, so work on that too.