Roosevelt was elected in Nov 1932 but did not take office until March 1933.
During the presidency of Hoover, many banks had gone bankrupt as businesses were unable to pay back loans. Millions of Americans had lost their savings.
"The Hundred Days" 4th March-16th June 1933 - Special session of congress:
Roosevelt closed all the banks for a "four day holiday" and passed "The Emergency Bank Relief Act" - Only banks which were thought trustworthy were allowed to reopen, backed with loans from the governemnt. The government guaranteed the money would be safe due to the Federal Deposit Insurance Corporation.
This restored confidence in the banks, at the same time Roosevelt acted to restore confidence in stock exchange as government agencies oversaw activities preventing bad/risky practices. This helped people to resume trading.