How do I pass data between 2 forms? C#

public class Form2 : Form
{
   private void LoginButton_Click(object sender, EventArgs e)
   {
      using (Form3 form = new Form3())
      {
         if (form.ShowDialog(this) == DialogResult.OK)
         {
            // Sucessful login

            // You can get the username back here. I don't think you need the
            // password, though. Passwords are only useful in Form3's context.
            string username = form.Username;
         }
         else
         {
            // Login failed
         }
      }
   }
}

public class Form3 : Form
{
   // This property will allow you to get the username, eventually.
   public string Username => UsernameTextBox.Text;

   // This event handler should be attached to the Validated event
   // of PasswordTextBox and PasswordRepeatTextBox. It disables the OK
   // button if both entries do not match. There is no point in enabling
   // to login if these values do not match in the first place.
   private void TextBox_Validated(object sender, EventArgs e)
   {
      OkButton.Enabled =
         PasswordTextBox.Text == PasswordRepeatTextBox.Text;
   }

   // This event handler must be attached to the Click event of the OK button.
   // It sets the form's DialogResult according to the validity of the
   // username/passsword pair.
   private void OkButton_Click(object sender, EventArgs e)
   {
      this.DialogResult =
         (IsValidLogin(UsernameTextBox.Text, PasswordTextBox.Text))
            ? DialogResult.OK
            : DialogResult.Cancel;
      this.Close();     
   }

   private bool IsValidLogin(string username, string password)
   {
      // TODO : you have to implement an actual username/password validation
      // strategy.
   }
}