It finds a designated route. So you start from here you are going to there, along the way when you get to this junction you will take this direction, and so on until you get to where you are going.

Each route has nodes that are junctions and nodes that are not junctions, so if it is not a junction, it carries on the same route until it gets to a junction, and calculates the distance traveled as it goes.

That's all it does so far. Now that I have this bit working correctly, I can add the rest of the functionality in around it. :-)