because Codoforum is a PHP system it would be quite nice if we (ya me too lol) learn PHP. That way we are able to develop our very own plugins, themes but also other systems, apps or even a CMS.
There are masses of good sources to learn PHP online and also tons of books. I found a very nice free info page which is easy to understand, is supporting a clean way to learn PHP the right way and is easy to understand.
Here you go: https://phptherightway.com