Search allows you to search content created by tools within a site. It achieves this by creating an index of all content that other tools make available to the search tool. This index is updated automatically, so as content is added to the site, it will be indexed.
For example, if the site has an Email Archive, as emails are posted to the list, the content of those emails will be indexed and become searchable in the search tool. Or, if the site has documents uploaded to Resources, the documents will become searchable.
Search indexes many different types of content, including messages, web pages in HTML format, documents in DOC, PDF, or RTF format, spreadsheets in XLS format, and Wiki pages.