Where you place your feet on the leg-press can impact which muscles get trained the hardest. It's easy to load up the plates and press without consideration, however where you place your feet is actually an important decision. Most leg-press platforms allow you to place your feet high, low, wide, narrow, or any number of combinations in between. Which combination you choose can actually change which muscles the leg press targets, making this exercise extremely versatile!
Placing your feet higher increases the degree of hip extension and flexion while reducing the range of motion around the knees. You'll feel an increased stretch in the hamsrings and glutes, making them capable of a stronger contraction. In other words, if you want to emphasize your glutes and upper hamstrings when leg pressing, use a high foot position. Of course, this shift in focus is not absolute, you can't truly isolate one muscle over another, so your quads will still do a lot of the work. Also, since you're seated during a leg press, your upper hamstrings and glutes still won't receive the same activation you'd get with a standing exercise like a squat.
So in short, place your feet higher to place more emphasis on your glutes and hamstrings, however squats will hit them harder!
A lower foot placement reduces the degree of hip extension and flexion while increasing the range of motion around the knees. That means you get more quad activation and less involvement from the glutes and hamsrings. Keep in mind that increasing the muscular stress on your quads also means the knees get subjected to greater stress. If you have pre-existing knee injuries or pain, you may find this foot position uncomfortable and should be especially careful.
Again in short, place your feet lower down on the pad to target the quads, but be careful if you have knee troubles.