The U.S. Census Bureau is a government agency that produces several surveys; the two major ones are:
1- Decennial Census: What is generally called "the census" (or sometimes "Census of Population & Housing"). Survey of the entire U.S. population, performed once every 10 years (2010, 2000, 1990, etc. back to 1790).
2- ACS (American Community Survey): A more detailed survey, performed more frequently than the Decennial Census (different areas on a rolling basis). If the decennial census data is too outdated or not detailed enough, you may use the ACS instead. See: Subjects included in the ACS
Once you know which survey data you need, you must then choose which source from which to get that data.