You made and still make some confusions.
From the point of view of the execution place, the web languages divides in two groups: server-side (runs on the server) and client-side (runs on the user's machine - on the browser, more precisely).
- Java (trough JSP), PHP, ASP(.NET), Perl... are server-side languages
So: you want to work within the Web applications? You need to know minimum:
- Content language: HTML, XHTML, HTML5
- Presentation language: CSS
- Server-side languages: PHP
- Relational database management systems: MySQL
- Other techniques: AJAX
You may also (or alternatively) need of ASP.NET, if you intend to work with the MS technologies.
Even it is not widely used these days, Java can be used for Web applications. As I said: trough JSP :
I think that the most server-side combination used these days is PHP/MySQL, probably because both are open source.