It speaks for itself. By standing on top of a barrel and grabbing it, you fly into the air, and you can also position yourself on top of it in midair to jump.

That's known. It's a glitch that's used a lot for noslraK speedrunning(Karlson reverse). Can someone else explain how it works I'm too lazy

its just the 0,0,0 prop flinging glitch. the prob flings itself to the 0,0,0 position and by that boosts the player up into the air

It's also jump off of the prop in midair to allow for essentially a double jump.

watch escape 3 or escape 2 gunless for prop jumps