When fdr took office in 1933, what was his first major action as president? why did he do this ?

FDR's first major act as president was the Emergency Banking Act. Passed just  5 days after his inauguration, FDR did this in hopes of stabilizing the banking industry. At this time in the US, the Great Depression was in full swing and banks were struggling. This is because so many people were trying to take out their money from the banks that thousands of banks all over the country were forced to close due to lack of paper currency.

With the Emergency Banking Act, FDR declares a "bank holiday." This 4 day period allowed the federal government to start reorganizing the banks and to provide currency to those banks who needed it.