Tap the rolled scroll at the top left corner to display the tasks window. Tasks are passive quests. Each of them has a timer. Simply wait until that timer expires then collect the rewards. There are three types of tasks; personal, clan, and premium. Personal tasks reward you with resources and general items. Clan tasks are similar, but also give additional bonuses for your clan. Premium tasks are rare, and usually can only be active one at a time. When completed, they will reward you with gold and premium items. There is also a cooldown of a few hours before you can select another premium task. Always try to have a task running.