You can find the option for Social Login right beneath the MMOGA customers login.

Please choose the account you want to use by clicking on it.

You are now being redirected to the login.
Please enter your third-party account's login information there.
This is how the Social Login looks like using Amazon as an example:

After successfully logging in you are now logged in to our shop system and can place an order.

IMPORTANT:
We do only get transmitted one Login ID in some cases.
In order to send you both confirmations and products, you might get asked to enter your e-mail address once again.
In that case please make sure you enter it correctly. Otherwise your order(s) won't get completed successfully.