To learn more about PowerPoint views, see Choose the right view for the task in PowerPoint.
By default, PowerPoint opens in Normal view, displaying the thumbnails, notes and slide view. If you prefer, however, you can specify that PowerPoint open in a different view, such as Slide Sorter view, Slide Show view, Notes Page view, and variations on Normal view.
Click File > Options > Advanced.
Under Display, in the Open all documents using this view list, select the view that you want to set as the new default, and then click OK.