When answering a question like this it is important not only to know the facts about the establishment of the Nazi dictatorship but also how to marshall that knowledge so that it answers the specific question. This questions asks us "how important" so you should write your essay with a direct answer in mind. Either the use of legal powers were very important or they were quite important or they were not important at all. It might help to assert what you are going to argue clearly in the introduction to your essay as well as in your conclusion.
Next, let's think about how the use of legal powers lead to the establishment of the Nazi dictatorship. It is particularly important with a question like this to look at the dates (January 1933 - August 1934) and to double check that everything you talk about falls within this time period. You may even want to give a brief description of what Germany was like at in January 1933 and how it compared to August 1934. For this question about legal powers you may wish to talk about:
-The Reichstag Fire Decree (the Decree of the Reich President for the Protection of the People and State) 27 February 1933
-The Law for the Restoration of the Professional Civil Service passed in April 1933
-The Law Against the Establishment of New Parties of July 1933
Then you should look at evidence which suggests that other factors were important in the establishment of the Nazi dictatorship, even if you are going to conclude that legal powers were the most important factor. If you can fairly represent the opposite view to your own and then critique it this makes for a very succesful essay.
You might want to talk about factors such as
Chance e.g. the death of President Hindenburg in August 1934
the use of propaganda e.g. the Day of Potsdam which was held to demonstrate unity between the Nazi movement and the old Prussian elite and military
-the use of violence e.g. the Night of the Long Knives which secured Hitler’s support from the Army and the business community
Finally, in your conclusion you want to briefly sum up your argument and possibly even answer the question using exactly the same wording to make it clear to an examiner that you have engaged with the question. For example:
'To conclude, the use of legal powers between January 1933 and August 1934 was a very important factor in the establishment of the Nazi dictatorship. This can be seen from Hitler's use of legal acts such as The Enabling Act of March 1933 to consolidate his power. However, the use of legal powers was by no means the only factor. The Nazis also benefited from luck and their masterful use of propaganda as well as violence and intimidation tactics."