I wanted to try creating WPS service in geoserver on web application. I wanted to know reference links or some help regarding using WPS on web.
There are instructions for installing the Web Processing Server (WPS) extension to GeoServer here.
Just follow the link posted by @PolyGeo , the second page shows how to use it and provides an example on how to perform a buffer operation.
Even better at the end there is a link to the WPS Request Builder which is a web based tool for constructing WPS requests. This should get you started quickly.
Besides the suggestions that @PolyGeo and @unicoletti already provided, I found the Processing part of the OpenGeo Suite documentation to be the most helpful for starting to use WPS.
The out-of-the-box WPS processes available with the GeoServer WPS extension might not fulfil all your needs. In that case, you will have to develop your own WPS processes and take a deep look at the GeoTools API documentation.
Disclaimer: I'm also a beginner regarding WPS.