To pick a layout for your slide, select the slide in the timeline then go to the "Layout" tab in the tool menu.
There are four layout styles to choose from for your slides:
Fullscreen (perfect for title slides).
Split Screen (great for having text on one side, photos or icons on the other).
Caption (for superimposing text over an image or video clip)
Title and Text (works well with headings and sub headings)