Master slides can be applied to selected slides or to all slides of a presentation.
Open your presentation.
(Optional) To apply a master slide to multiple slides but not all slides: Select the slides that you want a slide master applied to.
To select multiple slides, pressCtrl in the Slides Pane while clicking the slides you want to use.
In the Tasks pane, open the Master Pages and click the master page you want to apply. The master slide is applied to the corresponding page or pages.
If you do not see the Task Pane, click View › Task Pane.