In only a few months it grew from 500 visitors a day upto 1.5 million users.
The level of popularity and notoriety reached by Chatroulette creates enormous room for niche random chat websites.
If you're new, the Lobby is a great place to get started.
Once you are connected you may have a chatting session with this unknown stranger, but at any time during the connection both you and the other user have the option of pressing "next".
If EITHER of you should press the infamous "next" button, the chat session will end, and another random connection with another completely different random stranger will ensue.
So, what this means for you is if you are particularly uninteresting or uninviting on the eyes, you may get "next"-ed over and over, such that you may find the service to be somewhat depressing.
DO NOT FRET, eventually you should find someone willing to give you the time of day!