I have installed Xmonad 0.10-3 Lightweight X11 window manager written in Haskell along with libraries and documentation on my Ubuntu 12.04 LTS system.
I expected some interface/menu to run this application but nothing seen. I am also unable to find the related documentation.
Please guide how to start using Xmonad?
If you've installed XMonad via the Ubuntu package, you should be able to select XMonad as an option when you log into your system in the same way that you would choose any other window manager like Gnome or Unity.
Once you're in, you'll find that the default configuration is highly minimal. I would recommend following a tutorial to start out. The XMonad site (http://xmonad.org/) has a variety of documentation, including this getting started tutorial: http://xmonad.org/tour.html.
A large part of the joy of XMonad is the ability to roll your own very customized configuration. I found that the best way to figure out what is possible is to take a look at what others are doing. The XMonad site has a page with screenshots and many different example configuration files: http://www.haskell.org/haskellwiki/Xmonad/Config_archive.
Or, you may be interested in checking out my own commented and documented configuration, which includes installation instructions and a walkthrough of its features. I have made this available on GitHub: https://github.com/davidbrewer/xmonad-ubuntu-conf.
Above all, give it a little time! XMonad can be daunting at first but once I got used to it I couldn't imagine going back to a more conventional window manager for my daily work.