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.
All the slides in your presentation will include the information you have entered in the slide master.