Where do I add code to function.php file?

Hello,

If you are talking about code for adding search form yo your site

echo do_shortcode( ‘[aws_search_form]’ );

than its depends on theme that you are using.

You must find where your current theme has search form and replace its code with AWS plugin code.

But there is another solution for you.

To the very bottom of your functions.php file please add code

add_filter( 'get_search_form', 'aws_search_form' );

function aws_search_form( $form ) {
    return do_shortcode( '[aws_search_form]' );
}

Us I say all delends on your theme but its can work for you.