ExpressionEngine’s Search Module has several individual tags that work together to perform searches and display search results.
The Simple Search Form tag allows you to easily add a single-form search field to your site. This allows you to have a simple search box in a sidebar of your site.
The Advanced Search Form tag allows you to display a detailed search form that will allow your users to make “power searches” to find the information they need.
The Displaying Search Results page details the tags available for controling how you display results from your searches.
In addition to the options you have available for selection on the Advanced Search Form, you can also narrow down your searches by using special syntax with in the search keyword field.