At very first you should read basic things regarding design basics, HTML, CSS, HTML Editor such as Adobe Dreamweaver, web design software such as Adobe Photoshop etc. because they are the basic requirement to build quality and good website.
And after reading basic things regarding them, do start to make web design from initial level such as make banner, simple logo, layout etc. through the help of online tutorials and other website’s design and design the same thing by yourself. After getting confidence in basic things try to design banner, layout by yourself by adding your creativity in it because practice is most important thing in web designing.
Refer this link http://webdesign.about.com/od/beforeyoustartawebsite/p/build_website.htm to learn how to build website step by step in detailed way.