One of the better resources for those interested in dealing with web-based solutions on a regular basis is Code Academy. They offer parts of their curated courses as freebies. Here is a list of some of their offerings:
- Learn JavaScript
- Learn Rails
- Learn AngularJS
- Learn ReactJS: Part I
- Learn ReactJS: Part II
- Ruby on Rails Authentication
- Learn the Command Line
- Learn Git
- Learn SQL
- SQL: Table Transformation
- SQL: Analyzing Business Metrics
- Learn Java
- Learn HTML & CSS
Code Academy started as a simple attempt to make technology easier for new learners to understand and has since grown to millions-strong userbase of grateful coders. While not all of the courses listed above are 'necessary' to understanding how websites work, HTML & CSS, Javascript, and SQL are all great places to start.
Don't pass up HTML, CSS or Javascript just because everyone says you need to learn Java, for example. HTML, CSS & Javascript are some of the most widely used languages and scripts today in websites. Additionally, HTML5 and CSS3 provide extra functionality such as animation that was previously only the domain of scripts. Today, PHP is used server-side more than Java.