Most economy class tickets do not include checked baggage. In this case, you will need to add it.
To add checked baggage, please tick the checkbox as shown on the screenshot below. The checkbox is located below the passenger's name and date of birth.
If you book economy premium, business class, or first class tickets, checked baggage is already included in the price. In this case, only use this checkbox if you need additional baggage (for example, 2 items of checked baggage is already included with your business class tickets, but you need 3).