I was in grade 11 in my morning math class. Our teacher told us something about a plane crashing into the WTC. I talked to a buddy at lunch about it briefly. We were not totally aware what was going on at the time.
By the time I got to my chem class right after lunch everyone was talking about it. The teacher let us use his computer to watch the videos on CNN.com. We were all amazed and there were a ton of rumors floating around the room about other planes heading to LA and stuff like that.
When I got home, I was glued to the TV. The images of the second plane hitting and the shots of the towers actually falling were impossible not to watch. I just didn't understand how something like that could happen.
My g/f (who I had not met yet) was at university at the time. I believe that she assisted in setting up beds in the university's gym for all of the stranded airline passengers who were stuck in Halifax at the time.
Its probably the defining moment of our generation. It has affected everyone who lives in America, here in Canada and pretty much everywhere else. Its basically our Kennedy assassination or pearl harbor.
Its had major affects on the following years and probably will continue to for years to come.