How do people use guns in movies or in episodes?

I've seen behind the scenes of many action movies but how do they make the gun look like its actually shooting bullets. If you may know the popular freddiew on youtube he makes a lot of action videos on youtube where he is shooting with a gun but even though the people aren't actually getting shot how does it look like they are actually shooting with a real gun. I am only asking this because I want to see how they make gun shootings sooooo real it amazes me.