The service supports sign-in via the following social networks:
On the login page, click the social network icon. If you sign in for the first time, a new profile will be created in the service linked to the social network account. If the link has already been made, you will be authorized under your profile. On the registration form the process works in the same way
If you already have a profile and want to link sign-in via a social network, then on the profile page you need to click the social network icon. If the social network account is not linked to any profile, it will be linked to the current one. If the account is already linked to another profile, it cannot be switched to the current one, and you will be authorized under the linked profile.