The search engine does take a bit of getting used to and it isn't exactly intuitive.

Mouse over the search tab at the top of this page, and then select from the list, the general type of information that you want to search.

Then click on the view all in card catalogue button.

Then select the particular set of records that you want to search, or refine and limit your search by use of the filters on the left hand side of the page.

Watch some of the tutorial vids.

http://www.ancestry.com/cs/us/videos