Well, say you want to make a login system, you would want form1 to close then your form2 (program people register on your site or need a pass/auth code to see)
Ok, so this is the code you would need.
Form2 myForm2 = new Form2();
You add this in main method (in program.cs) under form1 one.
That should help you if you made a login or auth system.