I just don’t get it - what’s the point of topographic maps?

I don’t understand what all of the point of topographic maps is. I mean, what is the reason for a perfectly good map, but then drawing all over it? I can’t for the life of me figure out how to read one of these maps, nor can I see the reasoning for it. Perhaps I’m just a little ignorant, bet even though, I just don’t get it. Is there someone out there that can perhaps tell me what the significance of all of the little "contour" lines is and what purpose they serve. Because I’m a little in the dark!