From the order page, click the Login button
(circled in red)
Underneath the Login button,
click "create an account"
Fill in your name, email address, and create a password. Click the "Create Account" button.
When you checkout the first time, there will be an option at checkout to save your
payment info for future purchases.
You will only see this option if you are logged in your account.
This does not show at guest checkout.