HOPEFULLY, I have put this in the right section - if not take my apologies!

I have what is probably a very general question - but I cannot find a definitive answer by searching the web, and I need some professional advice.

What do I need to know to be a junior web developer?

Here's the thing, in 2004 I graduated from a university with a certificate (2 years) in Computing. However, having only really enjoyed the web development part of my course - I abandoned IT and moved into sales, where I remain today.

However, I kept up with my web development in my spare time and self-taught myself PHP and MySQL. I do have my own website, which is competent, but it's primarily buffered with borrowed js code etc.

I would however like to move into web development as a career but I have a) no experience and b) a lack of understanding of what it is I actually need to know.

My skills extend to an in-depth knowledge of PHP, MySQL, HTML and CSS. I can easily build a website and CMS from scratch with no HTML editor or web design template. While I have the raw skills and understanding of the languages and how to use them - I don't understand the job of a web developer.

I also lack confidence putting together a portfolio as behind every website will show the same programming skills and languages, and I feel each should demonstrate a new skill.

I read about junior developers being mentored by senior developers, but I don't know if that means being physically taught new programming languages etc. and best practices.

I'm just a bit lost... I do want to do this, but I'm unsure what it involves - if that makes sense. But I am willing to put in the work.

If someone can help me to understand where I need to begin and what it involves and maybe point me in the direction of a good book, webpage, blog or podcast - I'd be very grateful.