The Exemplar Library typically showcases examples of best practices for the benefit of all users in a system. Admins, by default, are the only users who have the ability to add artifacts to the Exemplar Library; however, admins have the ability to enable this ability for Coaches in their system, as well!
If you have Exemplar Library privileges, then you can add any of the videos or files that you have uploaded to Talent to the Exemplar Library. You can also add any videos or files that other users have shared with you at 'High' Permissions.
If you do not see the option to add a certain video or file to the Exemplar Library, then you will need to ask the owner of the artifact to change your permission level to 'High' in order for you add it to the Exemplar Library.