HTML is the basic structure all of web sites. I begin with it and I have studied it many times. First the 4.1 version and then I learnt the new features about HTML5. It is simple and easy to understand, even though there are some tricks not very intuitive for normal users.
CSS is the perfect complement of HTML because it styles the void text written in web pages. Color, background, font, position, margin, … there are so many possibilities you can play with it.
JQueryUI (JQuery User Interface) is the fastest way to build complex widgets easily. For example, menus, buttons, progressbar, datepicker, spins and so on. It’s almost so important as JQuery.
PHP is the simplest and most complex way to create a website with a client side and server side. Although its code is not the most «clean», its efficiency is formidable, obtaining more than enough results.
Mysql is the king in relational database management. With its SQL queries to databases you can create all kinds of applications with data persistence. Many of the main applications used today have MySQL as a database manager.
Java is the object-oriented programming language par excellence. With its strict rules and delimitations, they make it a robust and safe language to make applications. Whether for web, desktop applications, mobile apps, … It works very well in any field and platform.
WordPress is a CMS for creating websites. Their way of creating, modifying and displaying web pages are different from what the web developer is used to. Don’t get carried away with its simple user interface, as you have plenty of scope for drilling through PHP.