HTML was developed to define document structure like headings, paragraphs, and lists to share scientific information. It is now widely used to format web pages using tags. HTML is important for web development careers and skills like creating websites, becoming a web designer, optimizing website speed and performance, and understanding other languages like JavaScript and PHP. The basics of HTML include tags for headings, paragraphs, line breaks, centering content, and inserting horizontal rules. Attributes provide characteristics for elements, and common attributes are ID, title, class, and style. Formatting can be applied using bold, italics, underline, and other tags.