A VB form is essentially just a class. A class is the design of an object, not the object itself. An object must be 'instantiated" using the class to have an object that can be manipulated, e.g. shown on the screen.
I suspect you have your VB project set up to use the one form that is visible as the "Startup Object". That causes VB to generate the code to instantiate an object using that form's design. So that is the one that is displayed because its "Visible" property is set to True.
Most properties of a class can be changed at run time. When you set the property in the form design you are just setting the default property. So any time an instance of the class is created it will already have its Visible property set and it will be...