Census Records contain an amazing amount of useful information. In addition to family membership, census records can tell you where your ancestor was born, how old he was when the census record was made, what his occupation was and much much more! Census records after 1850 are particularly helpful, providing a list of all household members. Before 1850, only the head of the household was listed and limited information about other family members. Also, regretfully, the 1890 census burned, an enormous loss to family historians! Here is some information from the National Archives http://www.archives.gov/genealogy/census/
It is often a good idea to make a print copy of the census record that you have discovered in your search, but sometimes it is equally easy to just make a paper copy. Rootsweb has forms you can use.
http://helpdesk.rootsweb.com/get_started/charts_forms.html
One way to look for an ancestor in a census index is through the use of a soundex code. The system requires substitution of letters for numbers. Here is an automatic soundex convertor http://resources.rootsweb.com/cgi-bin/soundexconverter
Here are a few state and county resources:
Miami County of Ohio http://www.tdn-net.com/genealogy/miamico.htm
Wisconsin and Michigan http://www.telusplanet.net/public/mtoll/wi2.htm
Massachusetts http://www.censusfinder.com/massachusetts-census-records3.htm