3x3x3 With Feet
3x3x3 with Feet, commonly referred to as simply Feet, is a WCA event in which the object is to solve a Rubik's Cube with only your feet. The solver may use their hands and/or feet for inspections but may only touch the cube with their feet during the solve.
Removal of Feet as an official event
In September 2017, a Delegate poll with the question "Should 3x3x3 With Feet be an official WCA event?" resulted in a 58 to 56 result, in favor of removing feet.
In November 2017, the Board agreed with a proposed plan: The format of Feet should be changed from Mean of 3 to Average of 5. One year after the change has come into effect, we will analyze the popularity again. Feet will only be kept as an event if more than 30% of the competitions in the last 12 months held Feet and more than 4.5% of the competitors competing in the last 12 months competed in Feet.
In December of 2018 the WRC publicly announced that feet did not hit the criteria to be kept.  The WRC notified competitors that their preference was to remove 3x3x3 With Feet from the list of official events in 2020.
On December 3rd 2019 it was officially announced that Feet would be removed as an official event from the WCA. 
Feet is the least popular speedsolving event
Feet single is the most improved category in an event, with an improvement of 95.07% improvement from 2006 to 2019.
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.