The procedure of systematically acquiring, recording and calculating population information about the residents of a state, often including characteristics like gender, race, age, and occupation. When each census is conducted and what information is available will vary based on the procedures of the government collecting the data, so it's usually helpful to read some of the About pages on census websites. Keep in mind that shifts from colonial government to independence, as well as changes in census practices, will change what data is available.
When conducting historical census research, it is common for multiple levels of data to be available. Typically census bureaus collect names, addresses, and demographic information about individuals or households, and then use those raw documents to generate demographic statistics. People focused on genealogy research or other work looking at individual figures may want to access the original questionnaires or records from the census takers. People focused on demographic questions (e.g. how many people of African descent were located in Mexico in 1860), typically want to access the statistical data. Sometimes the statistical data is published in a searchable online database; sometimes you must find the original monograph or book in which the data would have been published originally. Background and secondary sources often provide the name of the original published books of statistics, which can be helpful in determining if Oberlin or a digital source like Hathitrust provides full text.
Tip: Some Latin American census websites will offer English translations. In the even that they do not, Google Chrome can translate webpages into English for you as you browse.