I need to work with census data and don't know where to start.
There are a number of resources you can use to learn about and use census data. The ISSR Data Archive maintains a collection of census data covering many years and countries.
https://www.library.ucla.edu/social-science-data-archive/about-data-archive
The Census Bureau provides options for making tables and downloading reports, maps and tables.
https://data.census.gov/cedsci/
Other useful census data sites: