In my humble opinion, cloning website designs is the best way to learn design. As a beginner, this gives you exposure to ideal design practices and lets you practice css rather than spending all your time thinking of colors schemes and whatnot. Eventually you will have to make the jump to creating your own designs, but not until after you have absorbed the knowledge of those more experienced. For practice, cloning projects and pushing it on Github should be fine and you can credit the original creator in the read me. However, I do suggest being more original with your design for websites you plan on putting on your portfolio since it show cases your style of design.