High poly or low Poly

Karycho

Well, a im fresh 3D modeler,still learn maya and Zbrush.Because i am new at this, i am learning from tutorials. Some of the tutorial i meed high poly or low poly. What does that mean? Do i always need to do high poly character or low poly? And how to do that? Do i need to create first either high poly or low poly character and then convert or whatever to low/high or high/low?

Sorry i really don;t know how to explain this confusion:D