I created a Registration & login page in asp.net C#.not use the inbuilt control.it works fine with sql db?

but i need to display the user name when the user gets logged.. in new page..how to do tat ...I created a Registration %26amp; login page in asp.net C#.not use the inbuilt control.it works fine with sql db?
how should I know when I don't know the layout of your DB or the names of any of the important variables.