PowerPoint 2011 for Mac by default display the theme gallery when opening the application. If you want to use only the blank presentation then you can turn off this feature by the following methods.
Mark the check box with the label as “Don’t show this when opening PowerPoint” below the PowerPointPresentation Gallery while choosing the theme for your presentation.
Another alternate way to turn off the display of theme gallery is by using the option available as part of PowerPoint 2011 preferences menu.
Step 1: Click PowerPoint menu and Select Preferences from the list.
Step 2: Click the General Tab and navigate to the General Option section.
Step 3: Un mark the check box with caption as “Open PowerPoint Gallery when application opens“.
Step 4: Click OK to confirm and save the changes.