This teaches you how to do a ladder climb.
The only key being pushed here should be forward.
No jumping, no crouching (although you should make one jump initially to grab the first rung).
Grab one rung, pull up slightly, then let go of forward to fall back down.
Immediately after letting go, press forward again to grab hold of the next rung.
A good strategy for beginners is to climb two rungs at a time, then drop down a rung, climb two more, etc.
If you keep pressing forward as you are pulling up on a rung you will fall all the way down (and you won't
be able to grab anything until you land on the floor).
If you are falling down often, you should probably be letting go of the rung sooner.