How Many Monitors You Use?

I just started using two monitors and I don't know how I lived without it, I got a question though if anyone has figured out how to do it, like lets say im playing league of legends, how do I click on something on my other monitor without it alt tabbing me out of game, like is there some other settings area I dont know about? if you know how to do something like that please lemme know I've googled everywhere for it.