I find it funny that the lady is talking about not going low enough but she is squatting high anyway. Her squat is above parallel. Keep in mind that your bone has to be parallel not your quads or your hamstrings since these muscles differ in shape from person to person.

1)  Should we place the bar at the trap area?
Depends on you, and your goals. Higher bar - squat deeper. Lower bar - more weight. But if you're starting, I'd recommend putting it not on the traps (high), nor on the rear deltoids (low), but on your body's natural shelf, which is the groove above the scapular spine. You will have to practice to find this groove but you will, since it's above that horizontal bone on your upper back when you squeeze your shoulder blades together. The bar shouldn't be on the bone but above it on the lower traps/Rhomboid muscles.

2) You have to keep your chest out and shoulder blades together (back), as this will help you not lean over and turning the squat into a goodmorning exercise. Your torso will bend slightly forward to balance the weight though. This is natural. Your natural arch will come naturally by keeping your shoulder blades back and chest up. Grasp bar as close as comfortable. Secondly take a deep breath before every descent. This will stabilize your torso. Exhale either half way up or after finishing the ascent. Don't bend wrists, keep them in line with your forearms. You might have to widen the grip for this but still maintain tension on the upperback/shoulderblades.

3) They are safe from injury as long as you do what the lady tells you in the first video. Knees going past toes can be both ankle and/or hamstring inflexibility, but either way you have to drive with your buttocks.
Don't knee squat. Start by descending with your buttocks by driving them backward, just as if you're wanting to sit on a toilet. You will see you'll feel a stretch in your hamstrings if you haven't done this before but you'll get used to it. This is the proper way. Starting with descending knees will give you knee injury. When you go up make sure your hips are going up as fast as your knees, if you don't do this you might turn it into a good morning exercise and lose the squat's efficiency.

All in all don't use padding, the muscles that you will place the bar on (your choice) will adapt and you will feel them stronger and harder in about a week. Start by squatting with the bar only until you're sure you can descend the proper way, and then just add weight. Keep in mind that your back (erector spinae) will get sore. Make sure you will distunguish between muscle soreness and spine pain. Spine pain is never good and it's a problem in technique. Also have a friend watch your technique and also tell you how low you're going since you might not be able to tell in front of a mirror.

Btw I hope someone will make a sticky (hint!), and gather as much info from other users' posts and sticky it on how the squat technique in the advanced section.

LSU Tigers Coach Tom Moffitt Back Squat Football Workout	DQ

I like the tips given in this video, especially the attitude part. You have to have the attitude and mentality ready before you squat.

Your back should arch because you are contracting your erector spinae, if you don't contract it all the pressure will be on the spine (BAD!). So the way you contract it, it will take it's natural curvature while contracted.

like its not straight as I am squatting down. Is this what you meant by my torso bending slightly forward?

Hard to tell what the problem is, but your back won't be perpendicular to the ground if that's what you meant. Depending on the weight it can actually lean 45 degrees. This all depends on flexibility as well, that's why it's hard to tell over the internet. The only thing that I can say is what I said before: on the ascent make sure your back goes up simultaneously with your hips. And keep your chest up/forward with shoulder blades back! If your hips go up first then your back will have to lean forward, which should be avoided.

Another thing for flexibility is that you should try going to a wall, stay about 3-4 inches from your toes and facing it. Then you extend your arms straight like a stickman. And then you squat down without biting the wall, or hitting it with your knees This will help you accommodate with the hip drive and also torso position (i.e. not leaning forward)

Stick with this guys vids and should be fine

Mark Rippetoe: Intro to the Squat	DQ

But if one doesn't actively tighten his abs, he may hyper extend the lower back. This doesn't happen to a person who has train to keep abs tight as a natural reflex. But if you keep observing, I'm sure you'll find some people standing or walking with their back hyper extent and the abs sloppily push forward, especially high-heeled ladies - that is more of a potential problem for lower back even more than slouching. A natural arch is cause by balancing the pressure from the erector spinae and the abs.

I would recommend train more until a tighten abs become a natural reflex - even when walking or standing in line (like Scooby suggests). And also, the best way to push your abs tight before a lift is a Karate shout (don't be shy, shout out loud right before you go down, that should keep your core in check)

Ofcourse you have to. With squat virtually you have to squeeze every muscle on your body. But the most important are lat, abs, lowerback and glute.

Well, as I was advised, Squat and Deadlift need intensive focus on the form therefore more than 5 reps may somehow dangerous, because you may lose your awareness of the form when it's getting tough. But with even lower weight and get into the endurance range (15 or more) I think it's not harmful.