Every web page you visit is built from three layers that work together.
HTML gives the page its structure: headings, paragraphs, images, links and forms. It says what each piece of content is.
CSS decides how it looks: colours, fonts, spacing and layout, and how the page rearranges itself on a phone.
JavaScript makes it respond: menus that open, forms that check what you typed, content that updates without reloading the page.
Learn them in that order. Clean structure first, then presentation, then behaviour, and each layer becomes much easier to get right.