What exactly does a blow off valve do on an engine?

I was thinking it might have been some sort of contraption to release compression pressure so your engine didnt explode at lets say 8.5k rpms, but my pops seems to disagree and doesnt know what its for either.

a blow off valve relieves pressure in the charge pipes of a turbo kit. When you let off the gas, the butterfly on your throttle body closes and all the air that was going to your engine reverses it's path and heads for the turbo again. This isn't good, so people use a blow off valve.

couldnt had said it any better my self but ill try ............. jk

Ah k, thanks, is it true that a turbo also uses an actual fluid and thats what a waste gate is for?

a wastegate is used alot for smaller turbos to reduce lag and preventing them from spinning to fast at high rpm's
A wastegate is a valve that allows the exhaust to bybass the turbine blades within the turbo. The wastegate feels the boost pressure and if it gets to high i could be a sign that the turbine is going to quickly so the wastegate bypasses a portion of the exhaust around the blades so that they can slow down.

so no its not for a liquid its for exhaust gas.