How do I study census records from a city and decade?

Census records have different information, depending on what year. Plus, some states took their own censuses during off years. Those often contain more information than the federal census did. Here is a link to a page that gives you information about each decade, plus other schedules that enumerated other information such as deaths or agriculture. https://www.archives.gov/research/census As far as which site has the the most userfriendly way to search the censuses, I'd say Ancestry, hands down. And FamilySearch has a great page to directly access each census in Ancestry. The link is here. https://www.familysearch.org/en/wiki/United_States_Census

Here is a link which lists all the state censuses: https://www.census.gov/about/history/census-records-family-history/family-records/genealogical-resources/state-censuses.html There are no links to the actual censuses, but Ancestry and FamilySearch contain all of them. Use the catalog in both sites.

I hope that helps.