The process of developing web sites and web applications utilizes a broad array of technologies, and this can get quite complex. To keep things simple for the time being, there are two general, primary approaches to thinking of development, the "frontend" and the "backend".
The frontend generally consists of what the user sees and much of what the user is able to do.
HTML is Hyper Text Markup Language. HTML is not a programming language per se. Web developers use it to define the content and structure of "web pages." With HTML, what you see is what you get. HTML states what goes where. In Chrome, if you right click on a webpage, then click on "view source," you can view the webpage's HTML markup, its skeleton. HTML uses tags to denote the what. For example, a <p> tag indicates a paragraph of text in relation to other tags.
CSS refers to Cascading Style Sheets. Traditionally CSS not a programming language, though this is changing to some degree. It is however responsible for making the content and structure of web pages pretty and interesting. The browser software uses the CSS to manipulate the HTML. In Chrome, while still on the "view source" page look for the following tag <link rel="stylesheet">. Behind this little bit of code is a file of likely monstrous proportions which tells the browser software how to make the web page look, and to some degree, behave.
Javascript has been described as the programming language of the internet, and it is largely what is behind UX, or user experience. There are now alternatives to Javascript for this title, but we won't get into it here. Developers use it to create valuable user functionality and satisfying interactions. The genius of the technology is that it is shipped over the network from a server to the user's local computer. The browser software implements the Javascript code on the local computer to produce the desired behavior. Without Javascript, various web application interaction features, such as drag and drop, would be less available.
The backend consists of what the user does not really see, such as the details of a web application's database.
PHP (PHP Hypertext Processor) is the programming language that didn't start out as one. It can be thought of as a quiet workhorse in the back forty. Where Javascript gets shipped off to the local computer to do fancy local things, like create animations, PHP stays home on the server. PHP interacts with servers and other server-based technologies, such as a MySQL database. It is dependable. Without being too careful in choosing words here, depending on the source consulted, PHP carries between 50% and 75% of historical websites and web applications and continues to evolve and maintain a strong following. A very popular PHP framework, Laravel, was created right here in Arkansas by Taylor Otwell, who still lives here. Laravel is now used worldwide!
SQL (some say it means Structured Query Language, others say don't listen to those people) is not a conventional general purpose programming language, such as Javascript and PHP, but rather is a declarative language that allows programs to interact with databases, the storage units of the application world. If you interact with data on a small-scale or enterprise scale web application, SQL is likely to be operating in the background to CRUD things up for you. CRUD, by the way, stands for Create, Read, Update, and Delete...the basic database operations which SQL delivers.
Feel free to continue on with this LibGuide to view a variety of resources on these topics.