How to check validations for login and logout on silverlight .net programm

i am preparing application for my mobile..

  SILEVRLIGHT WPF...mobile appilccation


 
  i want to do validations for my page:
 
  mandatory fileld:   mobilenumber
  loginid: userid 
  password..



  can some one teach me how to do valiations for these before login into these page...

  i want to write the validatiosn for my applications.....i am new to this programming...i am leraning slowly programming language..


  some one helpme to do this validations check....

 i am using mysql database....


   thanking you.....

with regards,
Sree