The only thing you need to do is to Sign in normally
to your profile page and enter your Google, Facebook or Soundcloud
account id under the "External Sign In provider"
section and you will be able to Sign in to our sites
just by clicking on one of the buttons above.
If you are already logged in Facebook, Google or Soundcloud
you will only be prompted to allow access to your
How external sign in works? (knowledgebase article)