There is a search bar on the home page, and in the filters box on the top of search results pages. To do a text search, enter one or more keywords in the search bar and click return if you are on the home page, or Apply if you are in the filter box. You'll see a results page with listings that contain the keywords.
The steps are slightly different with a phone or mobile device. Follow this link to learn how to search with a phone or mobile device.