hmm... i dunno what to suggest in temr sof reference because most books teahc you how to use the languages rather than why yto use em. you'll find articlres dotted across the net regarding why to use and advatnages of. your brest ebt is probably using a little tool called google!

But for a quicjk summary:

html
is meaningful, sematic lanuguage used to render a webpage, the code is processed in the web browser and displayed.

css
is used to style html - because html should be semantic it should have no styling or aesthetic feature sin it - so css is to provide these. css is linked into html making it easy to update styles sitewide.

php
a server side scripting language (i think) used to generate dynamic content and used closely with a databzase such as Mysql. Iyt integrates well with html and can be used together in the same document as html.

xml I've never really experienced to be honest!

and JS I don't know too mcuh of either but I believe it is a client side language.

Corretc me if I'm wrong.