I purchased some DVD's and CD's etc to help with ground school for exams and found them even more confusing in some respects
Although they helped in some subjects , it was more beneficial to have ground school with my flying school instructors who could explain things easier - and clearer and very tolerant of my constant questions - if you dont grasp it ..... ask
And as someone else mentioned Youtube , brilliant for some ground school subjects I'll concur with that
I found the King DVD's easier than Oxford to be honest