A guy is a dude, a boy, a man, or really anybody. It's an informal way to refer to a person, especially a male. But a group of people can be guys, even if they’re all female.
Hey guys! Another meaning of guy comes from a guy rope, which is basically a rope that supports something like a tent to a pole. What a guy! So to guy means “to support,” or “tied to” and not just physically. It’s almost like “guide.” The word comes from Guy Fawkes, who famously plotted to blow up Parliament in 1605 and is still burned in effigy yearly on the British Guy Fawkes Day.