To enable this button, do the following:
As an Administrator, go to the Users tab in Account & Settings, click on Social media and tick "Allow sharing certifications on LinkedIn" (1).
Your users will now be able to easily share their certifications on LinkedIn when completing a course that leads to a certification. They will need to click on "Share certificate" button (2).
Once you click there the button will change to connect to your LinkedIn account (3).
The learner will need to login to his account using the credentials of his profile (4).
After he signs in, he will need to manually add the certificate details (5) and save to publish the certificate in his profile.