From The Document Foundation Wiki
The elements that will be common to all slides (graphics, header, footer, slide number, signature, date, ...) are inserted into the slide master.
- switch to the slide master with: ▸ ;
- choose the element you want to use from the menu: ▸ (this menu is only available from the Master Slide page);
- choose the items you want to appear in the slides using the menu ▸ and fill out the information in this dialog;
- insert any graphics you want to use:
- rectangle with gradient fill
- imported image
- send objects to the background by right-clicking on each and selecting ▸ . This step is optional because the slide master is applied to the background. You only will want to do this to help with the development of the slide master;
- format the title fields and choose sizes, fonts, and colors;
- add text (using the T icon in the Drawing toolbar);
- add more information using the fields menu ▸ ▸ (date, author, ...); and
- when the slide master is finished, go back into the edit mode by clicking the Close Master View button.