First, click the "Clients" tab:
This will bring you to the clients list, which is initially empty. You can click the button in the top right to create a new client:
Fill in the client's name, then click "Save". After saving for the first time, you will then be able to add additional details like a logo, addresses, client contacts, and artwork files.
Now you will see the newly-created client.
Now that a client has been added, you can create an order.