It's a pretty simple concept in that you have one switcher engine you put in the middle, and various rolling stock you put on different sections of the track.  In general, you put two cars on the mainline track and one on each branch for a total of five cars.  Then you pick two of the three branch line cars you want to switch out, and replace them with the two cars on the mainline.  It takes a lot of switching, and this is where the Timesaver got it's name because the idea is to do it in the most time-efficient manner.  It's a one-person switching puzzle that you can compete with others on who is the fastest.  Derailing or using your hands adds penalty time.  You can make it easy by adding only a few cars, or make it hard by adding more cars or specifying an order.  There are an infinite number of ways to set up and switch!