is there any way to create theme instead of using codegen command?

Actually I try to create a theme for Orchard cms using Webmatrix 3. When i was searching net I learned a method using Codegen command.

orchard>codegen theme MyTheme /BasedOn:Contoso

My question follows:
1. Why Should I use the Codegen command?
2. Is there any other way to create a theme for orchard site.
3. If so, what's the method?

You can find Orchard.exe under YourWebSite/Bin open it in the command line tools and you will be able to use the Orchard command line.

Another way to create a theme is adding to your solution a project under the theme folder solution. But to do that you will need Visual Studio and the Orchard code source. Of course I guess that you could create the theme just making the structure file under YourWebSite/Themes/ but I don't think that's the way to go.

You should use it because it's the easiest way to do a theme.