followed by MouseInfo methods being executed on the MouseInfo object that the field 'mouse' refers to. Please see the MouseInfo class documentation for the methods that you can use on 'mouse'.
If you want to know more about using the mouse I have an example with explanation here:
http://mrstewartslessons.com/move_actor_with_mouse.html
and I have a video lesson about it here:
http://www.youtube.com/watch?v=HCl_XGWYYmc
It is really not that tricky. Once you get the location of the mouse with the MouseInfo methods 'gexX' and 'getY', you can use the Actor class 'turnTowards' method on the shot to set its direction of movement.