Widgets »Search Widget
The Search widget adds a search box to your blog sidebar or footer, allowing readers to easily search your site for posts and pages you’ve written in the past. Here’s an example of what it looks like in the Twenty Eleven theme:
Note: Some themes have a search bar built into the header. In this case, if there is no option to remove it in Appearance → Theme Options, it is not removable. If you have the Custom Design upgrade, you can hide it using CSS.
Once you add the widget to your sidebar from Appearance → Widgets, you’ll see that you can customize the title (i.e. Can’t Find What You’re Looking For?):
What It Searches
The Search widget will return results from the titles and the bodies of your posts and pages, and from media titles, alt text, file names, and captions. It will not return results from widgets, comments, categories, or tags.