HTML (HyperText Markup Language) is the standard language used to create and structure content on the web. It allows developers to define elements like headings, paragraphs, images, and links, making it possible to build web pages that are both functional and visually appealing. By using tags, HTML organizes the content so that browsers can display it correctly. CSS (Cascading Style Sheets) is used alongside HTML to control the appearance of web pages. It enables developers to apply styles such as colors, fonts, and layouts, enhancing the overall look and feel of a site. With CSS, you can create responsive designs that adapt to different screen sizes, ensuring a great user experience across devices.