Replying to Question about two about two (almost the same) lenses

Hi!

So, I'm getting a bit more into photography using my mums old Nikon FG (SLR). She has two lenses with almost the same specs but I can't figure out what the difference is.

They're both 52mm prime lenses, with F2.8-22 (does that even exist on Digital lenses?)
They're both Sigma lenses and they both have a Hakuba mark on them (whatever that may mean...). One is a bit bigger and has 'macro' written on it. Obviously the most logical thing would be that it's a macro lens, but how does that work? As in, why is it different than the other 'normal' lens?