Question

Following Pearl Harbor, what did the U.S. government do after it declared war on Japan and Germany?

Answer 1

Answer:
This question is far too broad, you need to narrow it down, a lot.
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Step-by-step explanation:
In the first 30 days the U.S. concentrated on re-opening Pearl Harbor and figuring out how it would conduct a two front war. By January 1942 the government had effectively gotten the U.S. press to allow censorship of all war related material. The U.S. population did not know for months after Pearl Harbor how many men had perished on that day.
The government also go much of industrial America to change their production lines to suit military needs, i.e. all car manufacturers ceased production of cars for civilian use and converted many of their assembly lines to build, jeeps, tanks, aircraft and other military necessities.
The first full-scale U.S. offensive, of sorts, was the Doolittle raid on Tokyo. It was not meant for anything more than to tell the Japanese government that we could get to them when we wanted.
The U.S. could not commit any sizeable number of troops into action simply because it did not have enough to do so. And so from January through September the services spent most of its energy on enlisting new troops, training them and then positioning them for later deployment.
During those months, high government officials and ranking military leaders consulted with the allied nations of the steps they would take as the U.S. entered the war.

Answer 2

They sent troops, ships, tanks, guns, and all those war-needed materials to Europe, Asia and even Africa to fight off the Germans, Italians and Japanese people.