This type of cipher is one of the most modern and ancient types. A message is encoded by shifting the alphabet by a certain number of times. Then, the new alphabet is put. For instance, in a shift of 1, A=B, B=C, and so on, all the way to Z=A.
This message below is encoded by a shift of 1:
Dbftbs xbt opu b wfsz ojdf qfstpo
Try to decrypt it!