very short explanation.........
it's an electrical device that heats up on one side and gets very cold on the other. The cold side is used to cool the CPU/GPU or whatever where the hot side must be cooled by another form of cooling like a HSF or water block, and even on occasion a second peltier.
Kinda the extreme cooling, and if you're new to OC'ing as you said, I wouldn't worry about one yet........just watch those pro's use em.......it's like going to professional drag races! You Cool Boys!