To make a drum loop, you need two things. The first is a drum sample; this can be a sample of a drummer playing a pattern or beat, or of a drum machine; it can be a sample from a record, or something that was recorded solely for you to sample it.

After you have the drum sample, you need to loop it. To loop is two play again, over and over again. Looping may sound simple, like something you can do with a simple wave form editor, but to do it well requires careful attention to nuance, and a good feel for the technology you're using.

Looping was originally done with pieces of magnetic tape. A length of tape was cut, and then strung through a tape player, one end spliced to the other so that it literally formed a loop. Now there are pieces of machinery and software called sequencers, which can loop a sample electronically or digitally, giving the user much finer control with much less effort. Far from hindering the art of looping by making it easier to do, however, this has allowed for great leaps in electronic music, and hip-hop, and avant-garde, and whatnot.