如何根据要求完全自定义nopCommerce 3.50主题？

I am trying to make a eCommerce site using nopCommerce 3.5 and new in it, I've a demo site and have make totally same as the site. I know basic of C#, asp.net, HTML, CSS but i can not properly able to modify the theme. I've follow all the documentation for designer at nopCommerce site but that is not giving a proper concept. I want to 1.Adding custom links to Menu Bar items. 2.Adding different style like demo site in categories bar. 3.Allowing comparing products. And so on The demo site is I am trying to make a eCommerce site using nopC