How exactly do compression fittings work?

[Waterlogged]

Hey thanks. But how do they connect to the blocks for example. Do i just need to screw in the barb part of the fitting first and then attach the hose and screw it down? Also, do you think that these fittings are necessary or are they mainly cosmetic. I'll have roughly 2-2.5 gallons per minute of flow in each of my three loops...

They attach just like normal screw in barbs. As for "are they necessary?"...not really. They're mostly for those that want a secure connection without an "ugly" hose clamp.