Space Mechanics:
Prograde burn: Burning prograde (speeding up) increases the opposite side's height, this is crucial for reaching the moon's SOI
Retrograde burn: Burning retrograde (slowing down) decreases the opposite side's height, this is crucial for re-entering earth's atmosphere
Atmosphere crash: Going too fast in the atmosphere while launching/re-entering causes your rocket/capsule to burn up, make sure your capsule has a heat shield and a parachute to land or slow down with your engine
Landing: Don't use your parachute to slow down, since you won't have a parachute to re-enter back to earth or you could add side parachutes to your lander or using engines to brake, parachutes do not work on celestial bodies that have no atmosphere
Tip: By tilting there's a chance you save valuable fuel and gain horizontal velocity to reach orbit