Having an account is not essential as you can select Checkout as Guest to complete an order without logging in. Any orders placed as a guest require you to manually enter your address and payment information and will not be saved for future reference.
To speed up any future orders you can create an account which allows you to save your address details and store credit cards securely. Creating an account can be done as you checkout by selecting New Customer or Sign Up on the mobile site. You can also create an account at the link below: