To run the SimpleCalc App that Xcode created from its template do the following steps:
In the main Xcode window, click on the Run button as shown in the following screenshot:
If we watch the Xcode status panel after clicking the Run button, we will (very briefly) see some messages that indicate Xcode is building our App as shown in the following screenshot:
After the building of the App is complete, the SimpleCalc App will display its menu bar and main window. When the SimpleCalc App is running we can drag its main window around, click on its menus, display the About window, and quit the App by selecting Quit SimpleCalc from the App's menu as shown in the following screenshot: