Yaw/roll - affect on heading
For the side slip, try thinking of it like this...with left aileron and right rudder (for example) the lift vector is tilted to the left, so the aircraft is constantly turning to the right (you are after all producing more lift with the main plane than the tail to stop the nose dropping, right, so less lift at the tail...) and the right rudder is making the aircraft nose constantly go to the right. If you are putting in enough yaw to counteract the sideward a component of the lift vector, you are not changing heading...
The rest if the time you want to be balanced, using your rudder to counteract any aileron drag, slipping, etc.
What wide words have your instructors given you over tea and biccies on this topic yet? Or have they been 'too busy' and left you to the books?
Don't be afraid to ask questions any time! We never learn otherwise...
(Just to throw you a curveball, now go think about how tailless designs operate in yaw ;-) )