All a loop really is, consists of a rythym which can transition seamlessly and repeat endlessly. The art of loop making has existed since the very start of recording. It's an incredibly powerful tool in the arsenal of a producer. Nowadays it's so easy to make loops digitally. There's no excuses to not make hit songs if you're an artistic genius. All songs contain a basic drum beat that repeats constantly, this is a loop, and it's the most important part of a song.
To use loops simply make an rhythm that repeats endlessly, with no awkward transition breaks.
A lot of beginners make the mistake of thinking they have to play for the whole song, in reality the natural inconsistency of performing a whole song doesn't work. Loops are the only option. It's incredibly difficult if not impossible to sustain a rythym in an exact manner for the length of a song.
Anything with a heartbeat can make loops, but that's not to take away from the art of it. An expert loop maker can produce an astounding amount of amazing bits on a consistent basis.