Each turn in Pick a Pen: Reef, the active player rolls the five colored pencils, then chooses one and marks spaces on their individual player sheet. Each other player in turn drafts a pencil and uses it. Pencils show symbols on their different sides, and the symbols on top of the chosen pencil determine what players do on their sheets.
Each sheet shows colored dive locations in the reefs. You can have only one route per color, so if you don't yet have a route of that color, you start one at an empty dive location; otherwise, you extend your existing route of that color. The symbols on the pencil indicate how many steps you can color in and whether you have to go straight or can choose freely. If you reach treasure chests or coins on your route, you can color in bonus points on your sheet. The game ends when one of the players has colored a certain number of treasures or all of their coins.
You each have a score sheet of the same level, on which you color in routes from different dive locations. The starting player first rolls all the pencils, each of which has a different color. There are different symbols on its sides. They show how many steps the route consists of that you can color on your score sheet.
Pick a Pen: Reef includes three difficulty levels of player sheets, with sheets 2 and 3 featuring vortices and propellers that can hinder or help you in different ways when coloring routes.