Is there any option to access a function inside function.php through a url?
Like joomla has this.
Any idea?
Use ajax functionality of wordpress:
You can use nopriv actions for that. wp-admin/admin-ajax.php is the url for the ajax page of wordpress.
Or either you can make a template page which gives only content and create a shortcode and add to a specific page.
functions.php is part of the core of your theme and is automatically included.
to access your function, simply use it in your theme file, as such:
<?php myfunc(); ?>