After defining the structure of your form with the WinForms designer you can display your forms in code with two different methods.
Method - A Modeless form
Form1 aForm1Instance = new Form1(); aForm1Instance.Show();
Method - A Modal Dialog
Form2 aForm2Instance = new Form2(); aForm2Instance.ShowDialog();
The two methods have a very important distinction. The first method (the modeless one) shows your form and then returns immediately without waiting the closure of the just opened form. So your code continues with whatever follows the Show call. The second method instead (the modal one) opens the form and blocks any activity on the whole application until you close the form via the close button or with some buttons appropriately configured to close the form