When launching yourself into a backflip, you are using Newton's Law of Universal Gravitation. When going back, you are using centripetal force which is the outward and upward force in a backflip. While flipping your path is redirected according to Newtonian Mechanics. Once you reach the apex, no panicking! Safely plant your feet into the ground and stick it.
Backflips may look like one fluid movement, but there not. There are two parts. Part one is when the flipper initiates the jump. The flipper must use their arms and legs to reach maximum height. Part two is the rotation. The flipper tucks their knees and rotates. A backflip uses the law of concentration and angular momentum.
When doing a back flip, the gymnast tucks their body into a coin shape, so they are rotating around the smallest axis, hips. Also, the conservation of angular momentum is important. The equation for this is Iw. I is the inertia and w is the angular momentum. When you jump, you want to have the most w as possible to complete the flip. You do all of this so you don't fall on your face.
The difference between a flip and twist is a flip is a human rotation about an axis that runs left to right through the hip. A twist is a human rotation about the length of the body. When a gymnast starts a layout flip with angular momentum, a twist can be added without any extra torque and keeping the momentum constant. The key to this is inertia tensor.