A paragraph style is a set of attributes—font size and color, for example—you can apply quickly to an entire paragraph. Using paragraph styles ensures a consistent look for the text in your presentation.
Paragraph styles also make it easy to format text. For example, if you apply the Heading style to all the headings in a presentation, and later decide you want to change their color, you can change the color of the Heading style itself, and all the headings update automatically—you don’t have to change them individually.
Paragraph styles appear in the Format sidebar on the right side of the Keynote window, where you can assign shortcut keys to them. If you don’t see the sidebar, or the sidebar doesn’t have text controls, click in the toolbar.