If you want to open Form2 modally (meaning you can't click on Form1 while Form2 is open), you can do this:
using (Form2 f2 = new Form2())
{
f2.ShowDialog(this);
}
If you want to open Form2 non-modally (meaning you can still click on Form1 while Form2 is open), you can create a form-level reference to Form2 like this:
private Form2 _f2;
public void openForm2()
{
_f2 = new Form2();
_f2.Show(this); // the "this" is important, as this will keep Form2 open above
// Form1.
}
public void closeForm2()
{
_f2.Close();
_f2.Dispose();
}