Taken from Wikipedia.org:

Adventure has the player's character explore a mysterious cave that is rumored to be filled with treasure and gold. To explore the cave, the player types in one- or two-word commands to move their character through the cave, interact with objects in the cave, pick up items to put into their inventory, and other actions. The program acts as a narrator, describing to the player what each location in the cave has, the results of certain actions, or if it did not understand the player's commands, asking for the player to retype their actions.

Certain actions may cause the death of the character (player has three lives), requiring the player to start again. The game has a point system, whereby completing certain goals earns a number of predetermined points. The ultimate goal is to earn the maximum amount of points (350 points), which partially correlates to finding all the treasures in the game and safely leaving the cave.

Colossal_Cave_Adventure#Gameplay