For assess questions basically you talk about a number of reasons and then "choose" a reason/reasons which are most important. For example take last years HSC question "Assess the view that the collapse of the Weimar Republic was primarily due to the appeal of Hitler and his Nazi Party." In this question you would have to talk about how much the Weimar Republic's demise and collapse depended on the appeal of HItler and the Nazi Party. Its basically a "why did the Weimar Republic collapse" question, but its asking you to judge
how important Hitler and the Nazi Party's appeal were in the Republic's downfall. So you would talk about how important Hitler and his Nazi Party were, but you would also mention many other factors that contributed to the Republic's collapse and suppor them with facts and figures (for example, you could argue that the economic situation was more to blame and you could use the large support for the KPD as evidence that it was not only the extreme right but also the extreme left that benefitted). That's basically how you go about answering assess questions.
Evaluate is much the same thing. Again, look at last year's question: "Evaluate the significance of the Battle of Stalingrad in 1943 for the military defeat and collapse of Nazism in 1945." So here you would talk about teh factors that led to Germany's defeat with an emphasis on how important the battle of stalingrad adn teh victory for the Russians was (perhaps you could argue it was a signiciant moral victory but not much more?). You would then of course include other reasons why Germany lost, like conditions on teh homefront, failure to reach total war footing till late in the war etc.
If you need clarification please ask, I hope this helps
