You don't need to know bacground...although it may help you understand it better. All you really need to do is look for examples of Powerplay in the text. Chose 4 aspects of powerplay (they'll probably only ask you to write on 3 at the most, but do 4 to be on the safe side...), such as Personal Power, Psychological Power, The Power of Language, the Power of the Mob, etc (every school probaly does different aspects, it doesn't really matter what you decide to do...) and find examples and quotes from J.C on each of your aspects. Then find a piece of wide reading for each aspect, to relate it to.
And make sure you spell Caesar properly in exams! Heaps of people always spell it incorrectly, and teachers get really shitty!