There are two common ways to place the bar for back squats. Either you squeeze your traps together (the muscles at the base of your neck) to make a little shelf for the bar, or you place the bar down on your rear deltoids, basically behind your shoulders. The first of these is called a high bar squat, and the second is low bar.
If you’ve only been doing your squats one way, consider the other next time you’re looking for a variation. The high bar squat keeps your torso more vertical, and is more similar to a front squat. The low bar squat lets you use your back and butt a bit more, making it a little more like a deadlift. Both are great ways to squat, so try the one you don’t usually do.