There are a number of resources that can help you learn how to do business with the Department of Defense. A good place to start is the DOD Office of Small Business Programs.
The General Services Administration operates the System for Award Management (SAM) which posts contract opportunities and procurement notices from Federal contracting offices. Anyone interested in doing business with the government can use this system to search for opportunities. Opportunities include pre-solicitation notices, solicitation notices, award notices, and sole source notices. SAM is an official website of the U.S. Government. There is no cost to use SAM. You can use this site for FREE to: