how to use login form

Make the Splash screen the Startup form for your application. When the splash scren is done, make it open up your Login form. If login is successful, then you get the login form to open up your main form. Here is the basic outline

public class splashscreen
    {
        public splashscreen()
        { }
        private void AmDone
        {
            Form login = New formLogin();
            login.Show();
            this.Close();
        }
    }
    public class formMain
    {
    }
    public class formLogin
    {
        private void LoginSuccessFul()
        {
            Form formMain = new formMain();
            formMain.Show();
            this.Close()
        }
    }

Hope this helps