Make sure you have previously registered on https://reddit.com
To setup Reddit social login, go to https://ssl.reddit.com/prefs/apps/ and click on create an app…
Fill out any required fields such as the application Name, About URL (optional) and Redirect URL: https://yourwebsitedomain/wp-login.php/?action=social_login_authenticated&provider=Reddit
Click on Create app and at the next page you can find your Client ID and Client Secret there.
Enter the Client ID and Client Secret keys into Social Login plugin configuration and you’re good to go.