In each Level, you need to complete a set of Orders from customers.
You can view the active Orders on top of the Kitchen Board. For each item in an Order, you can tap the [i] symbol to view how you can get the item. In the Orders view, you can also see the rewards for completing the current Level.
Finish all active Orders to complete the current Level.
Tip: Always check the Orders list and see which items you already have on the Kitchen board - figure out which items you want to merge first, without crowding the board!