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.
In 2018, the WRC decided after a vote that 3x3 With Feet should be removed in 2020, with a WCA Board vote in early 2019. This sparked praise and anger in the community due to the mixed opinions of its worthiness as an event. An unofficial strawpoll was held on the matter and results turned out incredibly close, 51% to 49% in favor of removing the event.
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.