How to open the second form?

You need to handle an event on Form1 that is raised as a result of user interaction. For example, if you have a “Settings” button that the user clicks in order to show the settings form (Form2), you should handle the Click event for that button:

private void settingsButton_Click(Object sender, EventArgs e)
{
    // Create a new instance of the Form2 class
    Form2 settingsForm = new Form2();

    // Show the settings form
    settingsForm.Show();
}

In addition to the Show method, you could also choose to use the ShowDialog method. The difference is that the latter shows the form as a modal dialog, meaning that the user cannot interact with the other forms in your application until they close the modal form. This is the same way that a message box works. The ShowDialog method also returns a value indicating how the form was closed.

When the user closes the settings form (by clicking the “X” in the title bar, for example), Windows will automatically take care of closing it.

If you want to close it yourself before the user asks to close it, you can call the form’s Close method:

this.Close();