The squat is probably the most difficult exercise to master.
You might want to re-evaluate your form.
First of all, find a comfortable stance (most people prefer a shoulder width and powerlifters like the wide stance).
Start the motion by first sinking your hips into the full squat position (keep your ass popped out).
Be sure to keep your back arched, this means keep your chest up and out and keep your head up.
when you start to return to the top, do not let your hips rise too fast. If this happens, you run the risk of using most of your lower back. Keep the movement at a reasonable pace, and keep your torso erect.
If your lower back is sore, you might be rounding your back to a small degree. When I say rounding, this means squatting out of the hole with your back slightly hunched over. Prevent this as much as possible.
For extra lower back strengthening I personally recommend:
Reverse Hyperextensions
Regular Hyperextensions
Good Mornings
Top Deadlifts
Practice, practice, practice your technique. Once this is mastered, be prepared to experience gains in size and strength in the hips and upper legs. Good luck!