"you and I"
Kāua refers to two people, the speaker and the listener. Kākou refers to 3 or more people, the speaker, the listener, and others. In English we use "we" for both of these situations, but in Hawaiian, you can specifically exclude or include others besides the speaker and listener by using these two words. Because kākou includes others, it is sometimes translated as "all of us" or "everyone".
Notice, also, that sometimes when we say "we" in English, we might instead mean "me and others", but not including the listener. There are separate words for that as well, but they are not currently included in the short initial release of this course. Hopefully they will be in a soon upcoming expansion.