When placing some elements, for example: Door, Window, or Components, you may find it useful to load families that are not currently in you model. Additional families are loaded from the contextual tab of the ribbon
To load families while in the context of placing elements
At the top right of the dialog, under Preview, a thumbnail image of the family displays.
The family type is now available to place in the project and is set as the active family in the type selector.
The content library is located here by default: %ALLUSERSPROFILE%\Autodesk\RVT 2021\Libraries
If your office is using a different library of content in another location, your system may access that library by default. Contact your CAD Manager for more information.