I know most people have watched hollywood movies where somebody is knocked out with a punch and the person is out for minutes. I know knocking somebody out is possible but does it happen as often as it is shown in movies and is it as easy as that? I for one have never seen a person knocked out for real.

Depends on the force and point of contact. A blow to the temple might be fatal. Real life example BOXING

No. Like the name 'movie' everything is exaggerated to the highest level.
Another trope in movies is where a character smashes a glass bottle on someone's head and the person immediately passes out. Try it in real life and your opponent would look at you with a dazed confused look before getting enraged.

People get knocked out a lot in fights. Here in Nigeria our streetfights are not boxing based but more of gidibo which involves overpowering/subduing your attacker. If you watch American streetfights on youtube they are full of knockouts because boxing is their culture hence the average man on the street reverts to throwing punches whenever angered.

It happens. Have seen a video where a rapper got sucker punched and he passed out.