Many plugins don’t provide a documented way to access their functions from within PHP (e.g. when building a custom theme), but only shortcodes to insert in posts.
Is there a standard way of executing shortcode from within PHP as if it were part of the content? Like so (this is made up):
$gallery_html = execute_shortcode("{gallery}"); // this would return the HTML
// that the gallery plugin returns
// in the context of the current post
You can execute shortcodes using the do_shortcode() function