It includes the ability to convert point data such as building locations into circular areas representing a specified distance from that location (stored as a series of point records with a shared ID). You might use this to find the areas representing 5km from tube/subway stations, for example.
It also allows you to convert area (polygon) or line (polyline) data such as coastlines or zip code boundaries by enlarging outwards, subtracting inwards, or creating a "channel" either/both sides of the outline, according to a specified distance. You might use this to find the area representing 20 miles from the coast, for example.
The resulting geographic "areas" can be used as an overlay in the Map view.
Please be aware that buffering can multiply the volume of data by several 100 times, since each point can introduce many points to describe the area around the point/line. Also note that while point buffering is true to the Earth's shape, line/area buffering is done in Euclidean space, so is only accurate at the local level and becomes completely inaccurate when you have areas/lines covering a large proportion of the world. Only supports WGS84 coordinates.