how to get user name and password from table in .net

You can do it.....buddy....

  But here you does not mention WHAT backend you are using to store DATA...
     
 you just need to KNOW MORE about How to Pass Queries to Database

  if you want to make any selection from DATABASE , there a SIMPLE way to do it..   just a single liner code....

  e.g. (in your case it is like )
        SELECT user_name, password  FROM  yourTableName

  This query will return all Usernames & respective Passwords from that TABLE
  then using any Conditional Statement you can verify whether Input Username &
  Password are from same row or not. Means....Input parameters are correct or not, if not it will return error.

Note:- i give solution as considering you are using any SQL Database Server to store your data.

here are few link which help you to KNOW MORE about using Queries...
   http://www.w3schools.com/sql/sql_select.asp
  http://en.wikipedia.org/wiki/SQL
  http://en.wikipedia.org/wiki/Language_Integrated_Query
  http://www.tizag.com/sqlTutorial/sqlqueries.php
 

try this ,
http://www.c-sharpcorner.com/uploadfile/abhikumarvatsa/simple-login-project-in-Asp-Net/

http://rixxtech.blogspot.in/2011/01/how-to-create-login-form-in-c.html