Questions abot 'themes' in Phil Sturgeon's template library

[eluser]Unknown[/eluser]
Hello, everyone. I'm a complete newbie in CI and MVC. I have downloaded Phil Sturgeon's template library but I don't quite understand the role of the themes. What is the difference between the layout and the theme, when do we use themes and how do we use them? I did't find anything about these in the documentation. Thanks in advance.

[eluser]umefarooq[/eluser]
layout is the part of any theme if you are using any theme for your project if you are not using any theme for project then you can use only layout just put layout file in main view folder, themes are combination of css,js and images files and folder