Grab the pole from the side. If you fail you should respawn facing where you need to grab. It should rocket you to insane speeds. As the text implies, its insanely difficult to actually get anything controllable from this. Its more of a demonstration than a useful technique, but you can finish the map in ~2-3s if you get it right

Hoe do you beat the challenge at the start behind everything

Both that swing and the swing after make use of the fact swings maintain height when using them. Follow through with your swing and jump on the other side to regain the height to make the jump you are talking about.

Jump onto one of the two side bars and spam space to do the jump after that.

The swing after that demonstrates how if you jump during a swing it can potentially gain speed from bonking you head on the pole itself.

could you please explain to me what I am supposed to do for that swing right after the first checkpoint?