For a start, post code in [code] tags, not as images.

You have an Add push button in the WT Designer UI that you completely ignore: this button does nothing as a result. You then create another push button labelled Add and show it as a top-level window (look carefully when you start the application) and connect it to your slot. When you click the free-standing Add button the second form is shown.

The second form shows overlaid in a messy fashion on the main form's content because you have given the second form the first form as parent: you probably don't want to do this if the second form is supposed to stand alone.