code for identifying current user of website

Question

hi Team,

 

     I am new web application , recently i had created one website using using asp.net with c# and sql express as back-end  for online attendance, in that i have crate a separate log-in for instructors  

My requirement is that i want to identify which user is currently loged in to the instructor page   and want to display his name on the same page like welcome <instructor name>  . kindly help me