The generator tag is used by WordPress to identify which version of the software you are running. Read about how this could be making your site less secure.
Child themes provide a convenient way of making changes to your site which are not then overwritten when you upgrade your WordPress theme. Find how how to use them in this post.
Shortcodes are a means of running custom code from the WordPress editor. Find out how to create your own shortcodes using PHP.
Regardless of which system I work on, I always tend to use the same wrapper functions for debugging because they are easy to use and reduce the amount of typing.