Think of a relay. The farsta is a mass-start event. You do two or more loops. But, instead of changing runners, the same person does every loop. During the course of the loops, you will go through some shared controls. That is, on each loop, you will visit some of the same controls you visited the time before. But, you will enter them from different controls and leave them for different controls. By the time you complete the entire course (all loops), you will have run exactly the same legs as everybody else on your course. But, you will do the legs in a different order from most other runners. There can be 8, 16, 32 or even more different combinations!