During the routine programing in the .NET Framework while applying the Window Form C# Application, many forms are needed at the time. You will have to apply the series of many forms for making the applications. So, you must understand the process of adding the new forms in the Windows Form C# applications.
Let’s have a look upon the simple and the fundamental procedure to add the new form while the older form is still open. It is s 3 step process which is explained in the tutorial.
Tutorial
1: When the Form1 is already open, to add an additional Form2 in the application, just right click the mouse button in the ‘Solution Explorer – WindowsFormsApplication17’. It will open up a left ward popup menu.
2: In this leftward popup menu, move your mouse cursor over the ‘Add’. It will further open up a new left ward popup menu.
3: Click the ‘New Item’ in this left ward popup menu. It will open up ‘Add New Item’ interface prompt in new window.
4: In the ‘Add New Item’ interface prompt, click the ‘Windows form’ and then click the ‘Add’. 
5: It will open up the new ‘Form2’ in the ‘WindowsFormsApplication17’ with the name of ‘Form2’.
Similarly, you may add many such forms in the Windows Forms Applications for working upon the Apps.
Stay Tuned for further tutorials upon the Windows Forms Applications.