Simply click on 'Log in / Register' at the top of the page, select 'Log in with Facebook' or 'Log in with Google+' and follow the steps provided.
The login via Google+ and Facebook is currently not available. Please create a user account using the link 'You don't have an account yet? Register' at the very bottom of the box.
If you have previously used Google or Facebook to log in, please send an e-mail at firstname.lastname@example.org or use the contact form - "Answer not found? Ask a question here" - below this article.