It is a sport, in which competitors run, (or walk if they feel like it), around a course with the aid of a map and compass, against the clock. Except on novice courses, an important element is that the terrain presents a choice of route to reach each control point, thus presenting a mental as well as physical challenge.
A number of control points, the amount depending on the length of the course, are marked on the map. At each there is a marker flag, usually a Sport Ident (SI) dibber box or, perhaps, a traditional pin punch.
You punch or dib at the control point and move on to the next one in sequence
until you have completed the course and you reach the finish. Here you go to the download area to download the
data from your SI dibber.