I've only done quite limited exercises with the free weights we have, and have decided to learn to do the full squat.
However, when I follow links from here to a couple of different recommended weightlifting sites, I get conflicting advice on form.
On exrx.net, they say
"The primary danger to the knee occurs when the tissues of the calf and thigh press together altering the center of rotation back to the contact area creating a dislocation effect."
and
"Contrary to propaganda to the contrary, prominent weight training authorities demonstrate the squat with the knees flexing forward at the same distance as the hips flex backwards. Fredrick Hatfield, Ph.D., the first man to squat over 800 lbs, recommends the knees to extend over the feet with the back more upright for quadriceps development. "Strength Training for Young Athletes" by Steven J. Fleck, PhD and William J. Kraemer, PhD, illustrate parallel squats with the
knees extending beyond the feet (knees moving forward with same magnitude as hip moving backwards)."
Whereas on stumptuous.com she says:
"At the bottom of the squat, hamstrings make contact with the calves."
and
"Think about keeping your shins roughly perpendicular to the floor and your knees roughly behind your toes."
So, you see, one recommended site says to touch your hamstrings to your calves, while the other says not to. One says to keep your knees behind your toes, while the other says to let the keee go past the feet.
Which is it?
I don't want to garbage my knees doing it the wrong way.

And they sure do lots of crackly popping noises doing the full squat just with my body weight. I haven't even tried with a broomstick yet!
Also, how necessary is it to keep your back arched? I really can't seem to hold it arched all the way down- it straightens up some at the bottom. Is this going to hurt my back?
I really want to start doing lots more with my weights . I'm only doing about 4or 5 things with the actual barbells right now, and the rest is just basically calisthenics with itsy bitsy 5 lb dumbells. The full squat seems like a good one to add, but I need some advice on how to do it right!