In order to get access to the game, you must register an account on this site. Make sure when entering the registration form, you use the same username as the one you've set in your MCPE launcher, otherwise it simple won't work.
When you registered, you've received an verification email. Login on the homepage and enter the same code as written in the email. If you entered a wrong email address, you cannot play. We just don't like fake people.
Once you completed the registration, you can buy items and do other awesome stuff on the website.