The basis of web development and designing is HTML and CSS. You have to learn these both of these in order to start web development and designing.
Moreover, you can also start learning about some designing and prototyping tools like ADOBE XD or FIGMA. By these tools you can make the design of your web page and with the help of HTML and CSS you can convert your design into a web page which runs on the browser.
You can use python for the backend development for a website.