Search engine code?

Just look over the default theme. It has a search function builtin. Or if you just want to add a simple search form to a new theme.

<form method="get" id="searchform" action="<?php bloginfo('url'); ?>/">
<div><input type="text" value="<?php the_search_query(); ?>" name="s" id="s" />
<input type="submit" id="searchsubmit" value="Search" />
</div>
</form>

Here is a good place to start learning about wordpress.
http://codex.wordpress.org/New_To_WordPress_-_Where_to_Start