Norms are social conventions that we pick up on through observation, practice, and trial and error. We may not even know we are breaking a social norm until we notice people looking at us strangely or someone corrects or teases us.
I can relate this to my knowledge I gained from my sociology class. Social norms are things that we are taught throughout our life through society. As we start to follow these norms we may also forget some of the other ones. We use peoples body language to tell us if we are following the norms when we are out in public.