I need some help #gunstr

I have my AR-15 mostly built but there are some nagging questions I haven't been able to find answers to online.

My biggest question is how a clamp-style free float barrel is supposed to be installed. Are you supposed to crank the screws hard enough to pinch the metal together, or is there supposed to be some kind of tension piece that goes between them that I'm missing?

Second question is what in the hell does this little tiny screw supposed to go to?