There are a few other things you may want to do while editing the master and layout templates:
Insert a new custom layout — To add a new custom layout to a theme, click the New Slide button. To rename a custom layout, right-click the layout in the list of layouts and select Rename layout.
Duplicate a layout — To duplicate a layout template, right-click the layout in the list of layouts and select Duplicate layout.
Delete a layout - To delete a layout, first select the layout from the master slides. The slides using this layout will be highlighted in yellow in the thumbnails on the left. Either delete the slides using the layout or change the layout for the slides. Then you can delete the layout from the master slides.
Insert a placeholder — To add placeholder text, click the Insert menu, select Placeholder, and choose to add a title, subtitle, or body text placeholder. A layout can have one title and one subtitle placeholder, but as many body text placeholders as you’d like.