The depression began in 1929 and lasted for about a decade. the main reason for the Great Depression was the unequal distribution of wealth throughout the 1920's, and the extensive stock market speculation that took place during the latter part that same decade.
http://www.gusmorino.com/pag3/greatdepression/The Great Depression badly affected the American people because there wasn’t a welfare system for unemployed workers
. Between 1929 and 1933 money income fell 53% and as a result, demand fell considerably. This led to lower levels of production and an unemployment rate of 25% by 1933.
http://www.thegreatdepression.co.uk/effects-on-america/There are a couple different reasons how America got out of the great depression. First, the New Deal presented by Franklin D. Roosavelt helped give americans jobs. In the New Deal the government basically created jobs for the Americans who needed them.
Second, World War II. World War II also helped because it created even more jobs. Thousands of men could just enlist for the army. Though by the time World War II came around, America was already out of the worst of the great depression. World War II was more of an event that officially marked the end of the Great Depression.
http://wiki.answers.com/Q/How_did_the_US_come_out_of_the_Great_Depression