That's a very vague question and if you want a sensible answer you will need to let us know your level of ability with html, css, e-commerce sites etc and provide details of what you have in mind and what you have tried. We will need more than a one line intro.
Do you know html/css/css3/js/php/?
Are you building it from scratch?
Are you using a CMS with e-commerce package (if so does it allow customisation)?
What have you tried so far?