You just describe that part. The rules and dice come in when something you do might or might not have the result you desire. In role playing, we have a referee who is often called a gamemaster. The gamemaster is responsible for setting up the scene with a description of what is happening as the action of the game begins. They choose the adventure situations, present them to the players with as much description and verbal picture-painting as possible, and decide how the rules governing the action are interpreted.
Leadership is only half the job of the gamemaster, however.
The other half is role playing. The gamemaster does not play a single character on the players' team. Unlike Cowboys and Indians, where your players chose up sides and competed against each other, role playing games have all the players more or less cooperating. As the cowboys ride on, the Gamemaster trots out his best sultry southern drawl when the beautiful saloon girl tells them that no one else in town is willing to help them track down the renegade Apaches and bring them to justice. And, of course, the gamemaster speaks with the stern but fair voice of a proud leader when the Apache chief confronts the cowboys and tells them they've been tricked into pursuing his braves by the evil railroad baron, who wants the Indians driven off the land.