Two methods exist in Revit to document area; Rooms and Areas. Okay technically this is true for Revit Architecture (RAC). Revit MEP has Spaces and Zones too but this post is focused on RAC.
A room and its area is defined globally, affecting all room areas, by one of four methods.
All room areas are determined by the existence of walls or room separation lines. The following image has some rooms, note the "X" in each room. These are a room's reference sub-category, usually turned off in Visibility/Graphic Overrides, and the center of the "X" is the origin of the room.
Consider a shopping mall, think of Area as an individual store or tenant and rooms as the storeroom, bathroom, fitting rooms etc. as defined by the partitions within a tenant's leased space. If that relationship makes sense you have a sense of the application of rooms and areas. Another way to think of them is of a college building with a dozen classrooms for mathematics. Each classroom is a unique area while an Area can be defined to include all of the classrooms as a single area designated as Mathematics. I apologize for the overlapping terminology, we use "area" interchangeably for a number of things which makes it a bit like, "Who's on First?".
Rooms are fast and easy but universal, calculated by the same boundary location. Areas are defined by boundaries that you choose to define yourself. Areas combined with Area Schemes allow us to provide summaries using different assumptions, like gross area versus rentable (stock settings in Revit). Area boundaries can follow walls or be based on boundary lines that we sketch ourselves regardless of building elements. The Area tools are the most similar to sketching polylines in AutoCAD that many of us are familiar with except that we can schedule the resulting data very easily and have it update dynamically. More work to be sure but much more flexible too.
Something to keep in mind is Areas and Rooms are not aware of each other. An Area cannot tell us how many Rooms exist within its boundaries. This has always felt like an oversight to me. My feeling was amplified when the Revit MEP product introduced Spaces and Zones and Zones are aware of Spaces. They have the sort of relationship I've always felt Rooms and Areas should have. This means you can define tenants with Areas and create Rooms inside their space but an Area schedule can't summarize the rooms it has inside. Two schedules will have to tell the story instead of one.