An Order ID is the number system that Amazon uses exclusively to keep track of orders. They are 19 digits long with two dashes, with the following format (as an example, your order number will be different):

123-4565772-1234567

To find your Order ID, go to Amazon web site and visit:

https://www.amazon.com/gp/css/order-history/ref=nav_youraccount_bnav_ya_ad_orders

or select Orders from the menu at the top of Amazon.com:

Order ID is on the right:

Another way is via the "Your Amazon order" email Amazon sent you: