3x3x3 With Feet
3x3x3 with Feet, commonly referred to as simply Feet, is an official WCA event in which the object is to solve a Rubik's Cube with only your feet. The solver may only touch the cube with their feet during inspection as well as the solve.
3x3x3 with Feet is one of the most disliked WCA events due to it being highly unsanitary compared to other events. This has led to some people arguing that Feet should be removed from the WCA. However, there is currently no sign of the event depleting anytime soon.
Parts of the feet to use
Basically, you want to try to use your big toe to turn each individual layer needed while trying to hold down the other two layers with your other foot. By knowing how much pressure is needed to hold down the other two layers with your other foot, it will take practice.
Also, you could try to turn the top layer of the cube with your big toe while holding the bottom two layers with your other foot. It might work for you or not.
Try to solve the cube with the least amount of moves, so I would suggest using the Petrus Method or another method that uses the least amount of moves.