Use the Family Editor to modify existing elements or create new ones to meet the specific needs of a project.
All of the elements that you add to your Revit projects are created with families.
For example, the structural members, walls, roofs, windows, and doors that you use to assemble a building model, as well as the callouts, fixtures, tags, and detail components that you use to document it, are all created with families.
By using predefined families and creating new ones in Revit, you can add both standard and custom elements to your building models. Families also provide a level of control over elements that are similar in use and behavior, allowing you to easily make design changes and manage your projects more efficiently.
For complete information about creating, modifying, and working with families, see Creating Loadable Families.