The first thing to do is to click on Start Docking. As soon as you do, you will notice that it changes to a Pause Docking. The simulator is now running.
If you are using the simulator with the integrated throttles/shifters, you will want to click on the throttles just above the white neutral bar to begin moving the boat forward. If you are using the simulator with separate throttles/shifters, you will want to click on the top of the left or right shifter and then click on the individual throttles for more speed. This will start the boat moving in the forward direction. At slow speeds, the shifters are enough to steer the boat. For example, one shifter/throttle forward and one shifter/throttle backward will turn the boat in circles.
Practice trying to dock the boat in one of the available docks by just using the shifters. If it looks like disaster is looming, you can always click Pause Docking and plan out your next move before you click on the Resume Docking. (Unfortunately, there are no Pause Docking opportunities when you get on your actual boat!)
There is a new feature to position the boat when the before you Start Docking or reposition the boat when the simulator is Paused! Click on the boat to drag it anywhere on the screen (if you drag it out of bounds, nothing will work properly) and click on the wheel to change the heading of the boat.
If you end up in a precarious position, you can always click on Reset and start again!