We are ready to change theme when we have a HTML template. System always prefer a Gird Base template which is based on jQuery JavaScript Framework. You see an existing template to have some idea on overall structure.
A tricks is, simply copy an existing template and rename the folder then start chaining inside it.
So, Finally here is the steps to create a Theme.
1.First create theme folder(Without Special Character) in view directory (development/view/). For example rainbow. Create same in themeroot(webroot/themeroot) for necessary scrip directory(JS,CSS)
2.Now create definition, common, layout, elements, home, page.
3.Create definition file(info.xml) and enter author information. Once definition is ready then go admin panel (Preferences>Theme) and active it.
4.Now you can start with Layout, Pages
5.Create New Action Method for customize pages.
6.User with URI Manager, Site Setting, InformationSet, CategorySet, Interface Builder for advanced work.