wordpress中的[（特殊功能）]是什么，如何为我的插件启用它们？

I'm wanting to include a function into a WordPress page, but since WordPress doesn't allow the use of <?php ?> tags I cannot add the functions regularly.

I noticed when using a gallery plugin that it added [flagallery gid=1 name="Gallery"] to the page content (when editing the page in visual mode). Is there some way to set this up in my plugin?

Like on my page have [myPlugin category=myCategory] run:

function myPlugin($category) {
    echo ...
}

They're called shortcodes.

This link should tell everything you need to know to get started with them: http://codex.wordpress.org/Shortcode_API

Pseudo example:

function category( $cat ) {
    extract( shortcode_atts( array(
        'cat' => 'something'
    ), $atts ) );

    return "category is {$cat}";
}
add_shortcode( 'myPlugin', 'category' );