Autocad 2010 or similar question?

i'm new to autocad and we're learning how to draw a basic door in architectural units. i understand how to use the line tools and whatnot, i just can't get the set-up. it's in the right units but every time i type in to have a 3' horizontal line, it goes wayyy off the graph. how do i get the 3' line to be small enough i can see it on my screen without scrolling. i tried different scales but i'm not quite sure how to use those so that may be the answer and i'm just doing it wrong. any help would be appreciated.