Body weight squat, goblet squat, zombie squat, front squat, and back squat
Squat.
Quad
mainly your legs but and your back a little
The quads
the difference in the amount of force is getting over complicated, the front squat is just another variation of the squat. Do the one that you are most comfortable with. Always use a spotter or a safety cage when doing sqauts. Go as heavy as possible squats and deadlifts are the hardest exercises but you will see massive increases in all your body if you do them regularly
Yes, it is a secondary muscle (synergist/stabilizer) used in the squat. There is a link below in which you can get a chart of the muscles used in a squat: go down about halfway and you'll see the chart.
A good squat exercise is the front squat in which the bar is placed on the front of your shoulders rather the back (very painful but rewarding). The wide grip bench press strengthens your upper body well.
It is recommended to hold a squat for 20-60 seconds for best results. Holding a squat for longer periods can lead to muscle fatigue and strain. Start with shorter holds and gradually increase your duration as you build strength and endurance.
isometric
Box Squat is a variation of a squat where you sit on a box and squat back up.
A squat involves both eccentric and concentric muscle contractions. The lowering phase where you bend your knees and lower your body is the eccentric phase, while the rising phase where you extend your knees and stand up is the concentric phase.