The Assemblies category of Revit elements supports construction workflows by letting you identify, classify, quantify, and document unique element combinations in the model. You can combine any number of model elements to create an assembly, which can then be edited, tagged, scheduled, and filtered.
Each unique assembly is listed as a type in the Project Browser, from where instances of that type can be placed in the drawing either by dragging or by using the Create Instance option on the context menu. You can select an assembly type in the Project Browser or an instance of that type in the drawing area and generate one or more types of isolated views of the assembly as well as parts lists, material takeoffs, and sheets. Assembly views are listed in the Project Browser, from where they can be easily dragged onto project or assembly sheet views as needed.
Each time you create a unique assembly, a new assembly type is added to the Project Browser. A new assembly type will also be added If you edit an instance of an existing assembly type such that it becomes unique. In cases where the new or edited assembly exactly matches an existing assembly type, it is added to the model as an instance of that type.
For example, say 2 wall-window assemblies are created separately, using walls as the naming category. If each consists of the same type of window at the same position in a wall of the same type and dimensions, then Revit detects a match, and both assemblies are instances of the same assembly type. However, if one of these assemblies is created using windows as the naming category, there is no match, and a separate assembly type is created (assuming no other match exists).