The Confluence search engine is based on Lucene. It begins working as soon as you install Confluence and can build search indices on a wide range of document types: blogs, pages, comments, attachments, etc.
For more information about performing a search on your Confluence content, please see the documentation.
As well as using the search box at the top right of every Confluence page, you can also use the 'Search' macro to embed particular search results in a particular page.
For example, you could use the 'Search' macro to search for the word 'documentation':
Found 10 search result(s).
gives