PinkLotus.7618

Can someone please offer a simple explanation of what a rotation is? As I understand it, it's the order in which you press each skill... is that right? I've been to snowcrows and am just overwhelmed with their explanations. Is there a site that offers simpler options? Are rotations even necessary in PvE? I've made it through the story without any, but are fractals gonna kick my butt if I don't know mine? Thanks in advance!