Go here: http://coub.com/friends/find
You'll be able to access lists of your contacts from Facebook, Twitter and Gmail.
On the left of the screen, you can invite people by email.
Coub of the Day is the crowning achievement for any Coub user. It's chosen by our editors, factoring in likes and shares. It's posted to the feed of everyone who follows Coub Of The Day, and that's almost every user.