The squat is one of the most famous and used fitness exercise, but it is not as easy as it look to do it right.
Always check that your knee and your toes will track in the same direction. Keep the pressure trough your heels all the way. Do not round your back forward, especially the lower back area that should stay neutral. For older people, it is not recomanded to put loads on knees when positionned at more than 90 degrees. Therefore, squating on a chair (with was designed fot its user to have their legs at 90 degrees when seated), is a great way to begin with.
To become stronger, try to sit as slow as you can, and feel the pressure on your heels when standing.
Note: If you find the progression between level 2 and 3 can too drastic, try to put the heel of one foot on the toes of the other. If you are at the gym, you can use a TRX to help by pulling wit your arms to et up.