In a Calcutta, golfers bid, auction style, on the golfer or team who they think will win the tournament (you can bid on yourself or your own team, too). All the money raised through the "auction" goes into the pot. At the end of the tournament, those who "won" the team that then won the tournament get a pre-determined payout from the auction pool.
The precise rules of a Calcutta can vary from place to place; many tournament organizers employ software programs that apply odds and determine win-place-show amounts. Perhaps the simplest and most common Calcutta payout is 70 percent of the pool to the "owner" of the winning tournament team, 30 percent to the "owner" of the second-place tournament team.
Among other variations is one that allows a golfer to buy back half of himself or his team from the winning bidder. For example, your team is "won" in the auction by Team X; if this rule is in effect, you can pay half of Team X's winning bid back to Team X in order to buy back half a stake in your own team. If your team then wins the tournament, your team and Team X split the Calcutta payout.
The USGA's policy on gambling states that participating in Calcuttas can put amateur status at risk.