We have a set of guides to Census information that give more details on other aspects of the Census.gov website, other sites where Census data is available (especially useful for historical data or if the government shuts down!). The guides also include discussions of thorny Census-related questions such as comparability of data over time, changing definitions of race and Hispanic origin, and important geographical concepts. It's important to understand these topics in order to use data effectively and ethically.
This page from the Guides is especially useful for finding more in-depth help with Census data:
Here are some of Census.gov's tutorials and other user aides: