Revit Architecture 2024 tutorials for beginnersII Setting a work plane and reference plane(class-28) 

A work plane is a virtual 2-dimensional surface used as the origin for a view or for sketching elements. Work Plane Set or Show or Viewer. on the Architecture, Structure, or Systems tab in projects. on the Create tab of the Family Editor
Reference planes are objects that we use to create the form and the structure of our family file. So, if you think about a project, we use levels and we use grids to kind of lay out the overall forms of a project. Well, reference planes are going to serve that purpose in the family editor