Unlike a perspective drawing (below)...
...which mimics the view that we see with our eyes; plans, elevations and sections have no diminishing lines or vanishing points. Instead everything is flattened. A plan view is a horizontal cut looking down. Cut object, like the walls below are shown with heavy lines. LIght lines indicate objects that are below the cut line. Dashed lines indicate something above.
A section is a vertical cut through the building. Again the cut objects are heavy. Objects beyond the cut are shown with light lines. Dashed lines are usually not used. Sometimes tones are used to indicate shadows.
Elevation views are typically the exterior views of a building.