To signup/purchase a membership or other product, go to the signup page:
If you already have an account, click "log in" at the top of the page and proceed.
Select the product that you want to purchase and sign up for. If you are not already a member, complete the registration form at the bottom of the page.
Then click "Next" to save it. You will then be directed to the payment page to compete your purchase. Once you have paid, your account will automatically be activated and you will be able to access your subscription's membership area.