rails server vs preview method in Ruby On Rails - mad_chatter

Hi there
I was integrating mad_chatter in my rails application .After integration when i tried to start my rails server by rails server in terminal it starts the server in normal way but doesnot starts the thin server at socket given in config.yml file . now when I do my_app perview It starts the Webrick along with thin server at port given in config.yml file . Now the thing is in preview mode , server is not redirecting to any url even root url . and showing me error like below

Not Found
`/' not found.
WEBrick/1.3.1 (Ruby/2.2.2/2015-04-13) at localhost:3000

And when i run server by rails server it give me following error in firebug

Firefox can't establish a connection to the server at ws://localhost:8100/.

Can any one tell what is preview and why it's not redirecting to any url .Any reference to documentation will be appreciated