Russian roulette is an evil game of suicide. It is not by any means an online casino game, because its played with real guns and bullets just like it's depicted in the movies. Unless you're going to a casino so that you can wave goodbye to your life, don't try to look for russian roulette there, and if you do, then casino is probably not the place you want to go to.
The classic russian roulette game is played just like we see it on television. A six or seven bullet revolver is used by the competing parties, with all but one bullets removed. In western movies the producers will typically make use of a double action S&W or Colt revolver, albeit Russian officers of tzarist times were equipped with a standard issue 1895 Nagant, which is radically different from what's displayed in movies.
So, all but one bullets are removed from the revolver. The russian roulette then begins. A participant spins the cylinder, puts the gun against his head and pulls the trigger. There's one to five chance that there's a bullet in the barrel and if it is, the player would, indeed, blow his brains out. If not, the gun is passed to the opponent. As the cylinder is spun every round, the game is called roulette, even though, of course, there's nothing in it that resembless roulette other than the spinning cylinder part. Don't play with guns, play online roulette instead.