Justice normally boils down to two demands:
Fairness and equality are often talked about as if they are different words for the same thing, but in fact they mean very different things.
Fairness is the idea of people getting what they deserve. In a fair society, people who have clear talent and who work hard and who make a contribution to the public good would be recognised and rewarded. This might include nurses and firemen and even philosophy teachers. A fair society wouldn't reward talentless layabouts or people who do work that is destructive to the community (pornographers, drug-dealers, maybe hedge-fund managers or arms dealers). In other words, a truly fair society would not be an equal society, because some people deserve more than others and some people deserve less.
Equality is the idea of everybody being treated in the same way. In an equal society, everyone would get the same recognition and reward, for whatever they did: streetcleaners would be recognised as just as valuable as brain surgeons while doctors and waitresses would be paid the same. Something like this was attempted in Communist countries like the USSR and Cuba (in fact, Cuba only abandoned this policy in 2008). As you can imagine, a completely equal society would be an unfair one in many ways, because people who were talented or hardworking or who did valuable work wouldn't be rewarded for it - except of course for the reward of knowing they'd done a good job.
This is one topic in the Problems in Ethics section of the Unit 3 exam. If this topic comes up, the question could refer specifically to philosophical ideas of justice and the just society, the philosophical basis of law and/or philosophical justifications for punishment.