If you're familiar with Craps and Roulette, then Keystone shouldn't have much of a learning curve. The game is played by rolling three dice on a semi-circle table with sixteen "stones" along its perimeter. Moving toward the interior, you have spots for sixteen numbers (3 through 18), three groups (4-9, keystone, 12-17), black/red, diamond/oval, pair/run/triples, and four triple combinations. You can place bets on any of these spots with odds ranging from common (low payout) to very rare (high payout).
To kick off a game, you place a bet on one of the sixteen outer stones (the Arch bet). You're then allowed to make any interior bets (Inside bets) that you'd like, after which the three dice are rolled. Depending on the result of the roll, the game highlights the areas of the board in which all bets are winners. In addition, the stone on the perimeter that matches the rolled total is removed. Once either of the two farthest stones (3 or 18) or both of the center stones (10 and 11) are knocked out, the half-ring of stones collapses, all remaining bets are forfeited, and the game is restarted. If any of the other stones are knocked out of play, the game continues. However, if a total amounts to a stone that's already been knocked out, then the next stone to the left (on the left half of the board) or to the right (on the right half) will be knocked out instead. If it eventually makes it to the 3 or 18, the stones collapse and the game is restarted.
It's also worth mentioning that there are two alternative versions of Keystone: Jackpot Keystone and Bloodstone. Jackpot Keystone is identical to the original version with one small difference - if the first roll of a game is 3 (all 1s) or 18 (all 6s), then all Arch bets instantly win. In Bloodstone, you'll find yourself betting against the dice. Obviously it's pretty easy to place bets on the board that the dice won't usually turn up, but if you happen to be unlucky enough to bet on what ends up rolling, then you're penalized what you would have won with that same bet in regular Keystone.
There is some skill to Keystone, but leaving the game with any kind of profit is going to take far more luck than skill. If you happen to put a max bet on a roll of triple 5s at precisely the right time, then you're going to reap the rewards. A vast majority of the time, though, you're just going to watch your stockpile of gold dwindle. As with real-life gambling, all you can really do is play conservatively until your gut tells you otherwise. May your gut be wise.