You lower yourself by only bending your knees not at all by bending your back. Some will insist on squatting very low. Keep in mind that your knees have a range of strength and they are not very strong when they are bent low. If you go very low all the time you are stressing your knees ligaments unnecessarily. The idea is to work those quadriceps not strain your knee ligaments.
Squats are very popular and helpful but they have some drawbacks.
Therefore, in order to get the barbell on the back of your shoulders you'll need a squat rack. This is handy for safety too. It will catch the barbell if you fall or can't get up. A nice gym no doubt has a rack for squats but if you want to work out at home you probably won't have that luxury. A simple solution is to put some hefty eye bolts into a joist in the ceiling or a beam and hang the barbell by two ropes just a bit lower than you squat.