The Seven Card Stud Poker game starts off with each player getting dealt three cards; two of them face down and one of them face up. The person with the lowest card showing is then required to make the bring-in bet, with the player to their left starting non-forced action. This player has the option of calling the bring-in bet, completing the bet by making a raise or simply folding their hand. Action then continues around the table with each person getting the chance to call, raise or fold and once the betting on Third Street has been settled, Fourth Street is then dealt face up to all the players.
Now, the player with the highest hand is required to make a bet and if you are playing with a limit betting structure, they have the option of making a double bet if they pair the card they have showing. Players have the option of checking or betting until a person bets at which point they have the option of calling, raising or folding. Once the betting round action has been resolved, the whole thing is repeated on Fifth and Sixth Streets with two more cards being dealt face up to each player.
Once the betting on Sixth Street has been resolved, then Seventh Street is dealt to each player face down. A final round of betting ensues at which point players show their hands and the person that can make the best five card poker hand from the seven they have available ends up winning the pot.
The reason 7 card stud poker is so popular in the world today has to do with the idea that it draws on the popularity of 5 card stud poker. When poker was initially created, the stud games served as a welcome alternative to the popular draw games and in today's world the stud games once again serve as a welcome alternative, except this time it is to the board games of Hold 'Em and Omaha rather than to the draw games. People that want something different naturally gravitate towards stud and this is why many poker experts believe that stud games have the longest playability simply because of the fact that they represent the alternative rather than what happens to be in style currently.