The skip in curling is the teammate that throws the seventh and eighth stones for a team and determines the team's strategy. The teammate calling the strategy, and determining the types of shots to throw is known as the skip. The skip will tell the rest of the team the shot that needs to be thrown. As the stone is moving down the ice, the skip will tell the sweepers when to start and stop sweeping the stone. By sweeping the stone, it will travel straighter and farther, thus helping the stone reach its desired position.
The skip is allowed to assist their team in sweeping the stones anytime they desire. At some points in the game, the skip can also sweep the opponent's stones. When the skip is telling the sweepers to sweep or not, they are making sure that the stone is following the proper line (path), and has enough weight to reach its desired location. Although it may seem like the skip is just yelling, they are yelling to convey important directions to the sweepers.