The site-library is a Team which every users belongs to but you will not see it in your Team's tab in Tercen.
Each instance of Tercen (e.g. tercen.com) has a site-library Team.
As you may know, Tercen uses the Team's to decide what components (i.e. operators, apps, templates) are available. It is at the team level which you install these components.
If you install a component (i.e. operators, apps, templates) into site-library it is available to all users and therefore users have immediate access to the component.
You do, however, need admin access to modify it.
To install a component into the site-library:
Login in as admin
Click on Teams
Click on site-library team
You can now install, as you normally do, any component.