How to use Faultcode

Hello,

I have created a webservice with EJB session bean as Endpoint.
I have a hanlder class implementing javax.xml.rpc.handler, where i am varifying user login/password information in the Header.

Now i want to set up faultcode, JUST CANNOT understand how and where to set the FaultCode. Please help as i am new to webservices and try to understand it but cannot understand faultcode concept.
How to set up faultcode? or through exception etc..

Please provide some details if possible!!!

Any tips will be very helpful.

Thanks
Salman Riaz