using session for login and logout in asp.net

firstly open the "Global.aspx".

then create a function there
 protected void Application_Start()
{
//we give the name of the session  here and declare it null ..username is the name of the session
//we can change it according to our needs
Sesssion["username"]="";
}


now we can create the function where we are login as
function boolean login( string username, string password)
{
  // firstly we match the login details from the database.

if(username == logincredintialfromdb && password ==logincredintialfromdb )
{
// the values are matched here so are assiging the value to the session variable
Session["username"]= username ;
return true;
}
else
{
return false;
}

}