You can create an account and save your order on the first screen when you checkout. Here, you'll see an option to "Create an account and save your order?" - check that box and create a password. Now, when you complete the checkout of the order, an account will be created for you and your order saved for easy retrieval and re-orders in the future.
You cannot create an account in the system until you place an order, as accounts are assigned to orders, so there is no need for an account in the system without an order to go with it.