Since I suspect you haven't used ancestry databases before, a couple of tips.
Enter as much info that you know in FTM for the particular person.
Select them - in either Family Tab or Person Tab
Select the Web Search Workspace.
The search page will appear and the person and some of his or her data should appear already filled in.
Birth date - make it be +/- 5 years, add a location if you didn't enter it and know it.
Enter "Any Event" and enter a place where they lived. If they lived in a different place when growing up than when adult, enter multiple places.
Click on Search button (at bottom of page).
The first item listed will probably be an entry into ancestry.com trees by users. Ignore them.
If you don't see your census records floating towards the top, click on Census records in the left side of the page and select the year you want to look for (more recent or oldest you think you might find the search subject.
If you have a person with a name that was often spelled in different ways, you may have to do multiple searches or use the ? or * wild cards.