1) You need to choose a path through the network that starts at a certain node, called the origin, and ends at another certain node, called the destination.
2) The lines connecting certain pairs of nodes commonly are links (which allow travel in either direction), although arcs (which only permit travel in one direction) also are allowed.
3) Associated with each link (or arc) is a nonnegative number called its length. (Be aware that the drawing of each link in the network typically makes no effort to show its true length other than giving the correct number next to the link.)
4) The objective is to find the shortest path (the path with the minimum total length) from the origin to the destination.