The word modeling here can be used in it’s widest meaning as to creating the building and its documentation which will include steps of touching on all kinds of objects in Revit (whether datum, building elements, views or managing settings). “Modeling” can also be used in a narrower sense to refer to that process of creating the building elements which in Revit are in 3D but also in creating the draft views with details (2D) needed for the project documentation. In an even more narrow sense modeling can refer to just creating the 3D elements of the building (not including the work to create and populate sheets, the 2D drafting of details etc.).
As mentioned before, “Revit leans towards parametric modeling. Parametric modeling means that the 3D object that will be modeled are guided by parameters. They have meaningful relationships with other objects that imitate the relationships in the real world.”
When it comes to populating a project in Revit, we never start from zero, even if we might want to. Every Revit project is created from a template which already has stuff in it, like datum objects: levels, views etc. These datum objects are crucial as a lot of other objects we place in the project are related and positioned in relation to them.
In Revit, the content we place in the project is categorized into Families and Spaces. The last one includes room, areas and volumes. The latter includes almost all other objects (walls windows, 2d lines etc.). Families themselves are divided into System Families and Component Families. These two groups have different properties. System Families reside only inside a project while Component Families can be saved into a Revit Family file (.rfa) and reused in other projects by loading them. System Families can thus not be loaded in other projects but can be copied between projects.
Both System and Component Families can be further divided into 2D and 3D families.