You should restate your thesis, summarise your points and put some sort of closure which concludes your argument.
However, in the HSC exam, you would not score any extra marks for having a fancy conclusion, so don't spend too much time trying to perfect it. I've seen some high range responses that have a very comprehensive body with each paragraph taking up a whole page, but the separate paragraph for the conclusion is no more than 5 lines.
The conclusion should be there just to indicate that this is the end of your argument and most conclusions just reinforce the main ideas and organisation in the response.