Green Moon is a traditional first-person, point-and-click adventure game following the standards of Myst and other classics of the genre, but with simpler puzzles aimed at the casual market. The player assumes the role of the sole inheritor of an abandoned house, a place containing a spell book left by ancient magicians. The tome has clear instructions about what tasks have to be accomplished, and can be accessed at any time from the top-right corner of the screen. The objects found on each room have to be dragged and dropped on the inventory slots at the bottom, from where they can be used on parts of the scenery or combined with other items to perform an action or complete a task. The inventory space is limited, but it is possible to left objects on most scenes and pick them up again later.

The cursor is context-sensitive, changing from the default pointing finger to a grabbing hand when over one of the objects, morphing into a magnifying glass when hovering over a part of the scenery with a zoom view, and transforming into walking shoes when near one of the exit spots. The player moves between rooms by clicking on the exit hotspots, usually positioned over obvious places like doors and other openings, or by pressing one of the four interface arrows surrounding the central image. The main character can wear clothes and consume food and beverages by selecting an item with the left button, and pressing the right button.

The locations have hints written on pieces of paper, or visual clues on various photographs and other notes scattered around the scenery. As the tasks are gradually completed on the spell book, new types of magic become available at the bottom-right generator, allowing time-travel, teleportation, healing, invisibility and other special abilities. Later in the game, the navigator becomes available at the bottom-left to explore the moon, showing a top view of the lunar landscape peppered with several travel locations and other reference points.

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