An order is a document sent by a Salesperson to an admin, defining the contract start date, products, pricing, and product details for a given account.
The Orders screen can be accessed by going to Partner Center > Sales > Orders.
When a Salesperson wants to activate products for an account, that Salesperson will fill out the order form in the Sales & Success Center. The order is then delivered to your admins via Partner Center, where they can approve, decline, Resend it to the Customer, activate, and even schedule activation for the specified products.
Declined orders can be edited and resubmitted from the ⋮ menu on an account's Orders tab.
Click on this article link to learn more about the various order statuses.