They haven't really been featured in the anime yet. If you want to see them you'll have to read the manga.
Indeed. I was really curious about the hype for these two; I guess I'll read the manga. Just wondering though, are they in a relationship? :>
http://shingekinokyojin.wikia.com/wiki/Ymir
"She is in love with Christa, and her primary goal is to protect her no matter the cost. The two have a strong connection, and deeply trust each other even while keeping secrets. Her feelings are obvious enough that Reiner calls her on them, but it seems she has not yet confessed her feelings."
Pretty canon.