Available at the very beginning, your Shop gives you access to a general inventory of items and resources in the game, available to purchase in limited quantities each day.
[Shop imagery here]
The Shop resets every 23 hours, which means items will become available one-hour earlier than they were the day before - at some point, your shop refreshes will happen overnight while you are sleeping :)
The cost of items in the Shop are often used as a measuring standard, useful in figuring out whether an in-app purchase deal is worth the expense, or whether an Event reward is worth the effort.