Are you sure its form 1918-1945? I think you would only be looking at 1933-1945, because before the Nazis took power there wasnt any repression or terror (perhaps there was just after teh depression and in the early 30s, but it wasnt significant or of an organised form)...
The Nazis used a system of indoctrination to convince people that what they were doing was right (talk about Hitler Youth, propaganda, also banning of the Protestat churches and replacing them with and evangelical Reich church, League for German Maidens, use of scape goats for economic problems, etc.). Tey used systematic terror against opposition, adn you could talk of things like the kristallnacht and how the Jews had very few rights (just abot no rights by 1939), banning of various groups like trade unions, all opposition parties, youth organisatoins etc. You could also talk about repression as in harsh cencorship, for example judges and people of the civil service who disobeyed the Nazis were simply fired from their jobs, no freeedom of speech or information (jazz music was banned), etc. Lastly you would probably go on to say that it wasnt totally succesful because there was still opposition groups that remaines such as teh Edelweiss Pirates and a few others which I cant remember at the moment.
Hope this helps