These duties are essentially the time limit in which the murderers (ducks) need to get their murdering done. You walk around a map with a list of duties to take care of, which are essentially simple micro-games where you need to click or drag your mouse to do several simple things like clean a mirror or wash the dishes.
In GGD you're either working together to find out who the murderers among you are, or you are said murderer trying to get away with it. For anyone familiar with the game Among us, skip to the next paragraph. Goose Goose Duck (GGD) is an excellent social deception/deduction game.