RIA Services - how to call store procedure in WCF RIA Service

Hi Team

I have added project "Silverlight WCF RIA Class Library". I have used Entityframe work and added Domain service as well..

Now i want to accesss my existing Store Procedure in WCF RIA Service..

I am new in WCF RIA service. So i don';t know how to start building service. I just simply want to check user name password in database from silverlight screen. Simply login screen, if user is valid then want to print 'valid user' else 'invlaid user' .

Can anyone help me how to do this in silverlight with WCF RIA Service ?

Thanks in advance !!
Rohan Dave