HTML (Hypertext Markup Language) is used for putting content on a web page. With its tag-based syntax, you can add things like text, images, video, or audio to a page. However, without CSS (Cascading Style Sheets) code, your content will look plain and default to the browser's built-in styles.
The key to a great looking web page, is to use both languages in tandem. Luckily both languages are easy to learn - these are critical skills for any web developer. Once you have a solid grasp, you'll move on to other languages like JavaScript, which can do much more than display and style content.
Later, you'll also learn how to use JavaScript (and other languages) to generate chunks of HTML and CSS so that you can dynamically show and hide various elements on a page as needed. Before you learn how to do this, you must have a good grasp of the fundamentals first.