No, you don't, you can order as a guest without creating an account.
If you do decide to create an account it is very quick and simple and enables you to then view your order status at any time and also view previous purchases. Most importantly it makes placing future orders for things like replacement filters etc, much simpler and quicker next time around.
Once you have created your account, and have finished shopping simply go to the checkout, choose the method of shipping you would like and continue to payment. If you are happy with the order, confirm the payment and the item(s) will be dispatched to you.