Select a style from the Style Browser on the left side of the document window, or from the Style Browser available from the toolbar Style button.
To reveal the Style Browser sidebar, choose View->Show Pages and Styles. For more information on the Styles Browser, see The Style Browser.
Note: Styles are associated with the type of element you have selected. If you have selected multiple different types of elements (for example a panel and a caption) you will not be presented with any styles.