Rocketjump is a technique that allows player to jump very high. As the name suggests, it requires a rocket launcher.
Normal rocketjump[]
The all trick is to obtain the highest possible altitude. That requires a good timing of jump and shoot. Do a jump and after a very short time (0.15 sec) shoot a single rocket vertically down.
Double rocketjump[]
In this case you must properly coordinate jump and two shoots. Shoot a single rocket vertically up. Then just perform a normal rocketjump so, to make rockets hit ground at the same time.
Triple rocketjump[]
To perform it correctly 3 rockets must hit the ground at the same time. The first shoot must reach out to you with a bit more delay. Then behave like in the case of double rocketjump.
Wall Rocketjump[]
To perform a Wall Rocketjump, simply run into a wall and while still holding the movement keys, jump and shoot a rocket at the wall, downwards. It will send you up, and you will go back to the wall. Very repeatable, can be used to glitch some maps.