Excel VBA comes with a comprehensive object model which contains classes and objects that you can use to manipulate any part of the running Excel application. One of the most common objects you'll use is the Application object. This is a top-level catchall that represents the current running instance of Excel. Almost everything that is not connected to a particular Excel workbook is in the Application object.
The Application object, as a top-level object, has literally hundreds of properties, methods, and events which can be used to control every aspect of Excel.