The president submits a budget to Congress for the federal government every fiscal year (October 1 through September 30). Congress must then pass appropriations bills to provide money to carry out government programs for that year. Appropriations bills are usually divided up by type of program and agency into thirteen separate bills: Agriculture, Commerce/Justice/State, Defense, District of Columbia, Energy and Water, Foreign Operations, Interior, Labor/Health and Human Services/Education, Legislative Branch, Military Construction, Transportation, Treasury/Postal Service, and Veterans' Affairs/Housing and Urban Development.
The Congressional Appropriations Process: An Introduction (CRS) (PDF)
Overview of the Authorization-Appropriations Process (CRS) (PDF)
Appropriations and other useful information is available on the Appropriations Bills page