Wow, this is a big question. The full answer is very complicated, to the extent that many, many books have been written and continue to be written on the subject, but the short answer is "both." I'll explain in some detail what I mean and give you some sources that you can consult if you want additional information.

Prior to the stock market crash in 1929 and the beginning of the Great Depression, the Nazis had been a marginal force in German politics. The party had grown since Hitler's release from prison in 1924, but it was still on the fringes of the political scene before the Depression hit; the Nazis had polled around 3% in the elections for the German parliament (Reichstag) in 1928.

They made their first real inroads after the Depression began, using a combination of German nationalist and economic populist rhetoric to gain support among people who were disillusioned with both the political instability and the economic destitution of Weimar Germany. In the first elections after the crash, in 1930, they increased their share of the vote to almost 20% and won 95 seats, which made them the second-largest party in the Reichstag. The coalition government between the center-right Centre Party and the center-left Social Democratic Party fell apart, and the Reichstag was entirely dependent on President Paul von Hindenburg's emergency decree powers to legislate. The Chancellor, Heinrich Brüning, eventually lost his position and was replaced by Franz von Papen, who also couldn't gain support, and another election followed in July 1932. In the meantime, Hitler had run against Hindenburg in the 1932 presidential election, with Hindenburg defeating him decisively to win a second term.

The Nazis became the largest party in the Reichstag after the July 1932 elections, with 230 seats, but they were short of the 305 needed to form a majority. Once again, no one could form a stable government, so there was another election in November 1932; the Nazis actually lost about 30 seats in that election, but remained the largest party. During this time, Hitler had been maneuvering behind the scenes with both von Papen and major industrialists, and both ultimately supported Hitler's appointment as Chancellor, which Hindenburg did on 30 January 1933. Four weeks later, after the Reichstag Fire, Hindenburg issued the Reichstag Fire Decree at Hitler's urging, which placed severe restrictions on civil liberties and began a repressive campaign against the Communist Party.

Another election was held in March 1933, where the Nazis engaged in widespread voter intimidation and violence against left wing groups, but still came up about 50 seats short of a majority. They maintained control with a conservative coalition government with other nationalist parties, and Hitler managed to cajole his coalition partners and the Centre Party to vote for the Enabling Act later that month, which essentially gave him dictatorial powers and allowed him to rule by decree. Hitler began consolidating his power through a combination of pervasive propaganda and political purges of his enemies (including the elimination of any potential internal opposition in the Nazi Party on the Night of the Long Knives, 30 June 1934). After Hindenburg died in August 1934, Hitler became the de facto dictator of Germany, and held a referendum later that month (again, marked by extensive voter intimidation) to confirm this de jure, taking the well-known title of Führer.

Hitler gained control of the lower levels of German government and civil society during this time in a process called "coordination" (Gleichschaltung), where the heads of all of the state governments were replaced with Nazis, and all other civil organizations were forced to either appoint Nazi leaders or be dissolved. The Nazis also commenced their repression of political enemies (Communists, socialists, etc.) and Jews; the first concentration camps were opened during this period. This is the "by force" part.

However, there was also a carrot to go with the stick. During the next few years, Hitler embarked on an aggressive program of economic reconstruction and military buildup, financed by extensive deficit spending. This reduced unemployment and increased wages. There was also pervasive propaganda, reminding the public that the Nazis had ended the chaos of the Weimar era, eliminated the threat of Communism, revived the German economy and military, and rejected the humiliation of the Versailles treaty.

So, to cut a long story short, Hitler gained control of Germany through a combination of gradually consolidating political power at the top level and then enforcing Nazi control at the lower levels; repressing their political enemies through violence, intimidation, and eventually arrests and killings; and winning support from the German public through aggressive economic, military, and social policy, bolstered by a massive and incredibly skillful propaganda operation.

If you'd like to read more about this from people who are much smarter than me, there are a number of good books on the subject. Two of the best are Ian Kershaw's Hitler 1889-1936: Hubris, and Richard Evans' The Coming of the Third Reich. These were my sort of "introduction" to the subject as a graduate student, and I'd recommend them as a good starting point for you if you want to learn more about this subject.