The New Slide Button
To add a new slide, click on the New Slide button located on the toolbar in the top right corner of the window or select Insert > New Slide from the menus. A slide is added to your presentation and the Slide Layout task pane appears at the right of the screen.
By default, PowerPoint assumes that you want the new slide layout to be the Bulleted List layout. If you don't, simply click on the desired slide layout in the task pane and the layout of the new slide will change.
After making your selection, you can close this task pane by clicking on the X in the top right corner to increase your work space.