In order to add a new order, first of all, the Orders module has to be enabled. To do this, go to the project settings, modules tab and check it in. Then, go to your project and click on the Orders tab, then on New order.
Fill in the fields: add at least number, project, date and status, these are required fields. The rest (like description) is optional. You can add products to your order as well. After it's done click Save.
Please note you can add as many order lines as you need to.