HTML (Hypertext Markup Language) and CSS (Cascading Style Sheets) are two of the fundamental building blocks of the internet. These two languages are essential to creating visually appealing and functional web pages. In this guide, we'll take a look at the basics of HTML/CSS, how to write your first code, and some of the best applications for it.

Understanding HTML/CSS Basics
HTML is used to structure web pages and to add content to them. It is a markup language that uses a set of tags to define different elements on a web page. Each tag is enclosed in angle brackets, and the content is placed between the opening and closing tags.

CSS, on the other hand, is used to style web pages. It is a style sheet language that allows developers to specify how HTML elements should be displayed on the page. CSS separates the content and structure of a web page from its visual presentation, making it easier to modify the look and feel of a website.

Writing Your First HTML/CSS Code
To write your first HTML/CSS code, you'll need a text editor like Notepad or Sublime Text. First, create a new file and save it with an .html extension. In this file, you'll write the HTML code that defines the structure of your web page.

Here's an example of HTML code that creates a simple web page with a title and some content:

```
<!DOCTYPE html>
<html>
<head>
  <title>My First Web Page</title>
  <style>
    h1 {
      color: blue;
    }
  </style>
</head>
<body>
  <h1>Hello World!</h1>
  <p>This is my first web page.</p>
</body>
</html>