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: 
 https://guides.library.ucla.edu/census 
 https://www.icpsr.umich.edu/web/pages/