Oh jesus, no offence to you man, but if you didn't know that... Blizzard really needs to fix how questing and classes work so new players can LEARN to use all their abilities. I blame the super balls easy low level content for why you didn't figure this out earlier. :P
My worst experience was probably being a hunter in Vanilla, you have no idea how many times I forgot to get my pet off of follow or aggressive stance. I pulled so many mobs and wiped the group in those days hahaha