From The Document Foundation Wiki
Use the toolbar to create table:
- Define the layout of your presentation (with at least one slide)
- In a slide, click in middle square (where is says Click to add text)
- Click the "Table" icon in the toolbar
- Fill in the numbers of rows and columns you want your table to have
- The table is created with a dark gray background for the header row, and the body rows alternate light gray and medium gray backgrounds.