Friend points are given out when someone adds you. It is currently stationed(as of 3.0) in the community tab. If you add someone, you will receive 100 rainbow cookies, and your friend will receive one friend point(FP). Vice versa if someone adds you. As of 3.0, you need 2 FP for the Doge theme, and up to 15 for all T6 structures. As of the 3.8+ update, friend codes were removed from the game entirely.