To add a new form to your application, you don't need to create a new Windows Form Application. Typically, your application's default form is Form1.
Then right click and do this
Now, add form by selecting Windows Form
Set the event for the button in Form1 to something like this
private void button1_Click(object sender, EventArgs e)
var form2 = new Form2();
If you want to interact with both forms, use form2.Show(); otherwise, use form2. ShowDialog() is used to stall the caller form until it is closed.