That is a good question! Please look into the screenshots and the description given below. This will help you understand the game better.
Red exclamation mark: This means that the Customer is waiting to be served.
Green tick mark on the Table:
This means that the Order is ready to be served. You need to serve your customers by dragging the Dishes to the Table.
Coins, XP and Star: This means that your Customer has finished their meal. You need to tap on the Table to collect your reward.
Coins spinning next to your Chef Store: This means that the item which you have put for sale in your Chef Store has been sold.
Red exclamation mark on Shop icon: This means that you have unlocked something for your Restaurant. You can visit and see what you have unlocked.