The caddie should be familiar with the yardage of the hole so he can alert the golfer which club to use.
Fore or Forward Caddying
Though no longer available on most courses, "forecaddies" were once a necessary part of the game. Before the manicured grass that golfers are so accustomed to now, courses were often kept trimmed only by sheep. Due to the long grass length, finding balls was often a difficult activity. The forecaddy solved this problem by racing ahead of the golfer to spot their shots on the hole.
This type of caddying has the golfer and caddie walking the course together. Normally the caddie will walk in front of the golfer carrying the golfer's bag. The caddy also offers a variety of advice, such as suggesting a club for a particular shot, in order to assure the lowest possible score.
Caddies are responsible for marking the ball on the green. This helps the golfer know where to place the ball when it is their next shot.
A caddie can have the responsibility to be a hole reader. They will know how many hills the golfer must contend with, know what hazards are on the course and take wind and weather into account.
If nothing else, a caddie is there to be a friend or companion to the golfer. A typical round of golf lasts three hours. It is helpful to have someone to talk to during the course of play.