Learn as you go along. Google or ask people if you don't find what you search for. Start with a simple HTML page with an image, a few paragraphs of texts, maybe an unordered list to start with. Now learn enough CSS to add some styles. It won't look like much when you start, but it will soon improve, just be patient and slowly try to improve. Next, you can start with some simple JavaScript, e.g. to trigger an animation.
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but i did't know anything
Learn as you go along. Google or ask people if you don't find what you search for. Start with a simple HTML page with an image, a few paragraphs of texts, maybe an unordered list to start with. Now learn enough CSS to add some styles. It won't look like much when you start, but it will soon improve, just be patient and slowly try to improve. Next, you can start with some simple JavaScript, e.g. to trigger an animation.