Unfamiliar things are unknown or unexplored. On your first day at a new school, every single face you see is unfamiliar.
Traveling in an unfamiliar city is easier with a map or a GPS, and meeting the unfamiliar people who live there is easier if you speak at least a few words of their language. Some people love eating unfamiliar food — things they've never tasted before — while others aren't fond of it. When something (or someone) is familiar, it's known to you — the word shares a Latin root with family. Add the "not" prefix un-, and you've got unfamiliar.