Display users name once they have logged in:

First create a user class something like below,

public class UserProfile
{
  public string UserName {get;set;};
  .........................
}

then on successful login,just create one static user object like ,

static UserProfile userProfile=new UserProfile(); and assign the username

userProfile.UserName="XYZ";

then you can access that object in any form in your application(in your case on next form).

lblUsername.Text=UserProfile.UserName;