In the Current and Notes layout, you can see presenter notes underneath your slides. The thumbnails on the left are optional.
To advance to the next build or slide, tap once anywhere, or swipe toward the left. To go back, swipe toward the right. A nice extra in Keynote for the iPad is a “laser pointer”: Touch and hold on the iPad’s screen to show a red dot, which moves with your finger on the main display. Lift your finger and the dot disappears. This is very useful when you want to call attention to a particular area of a slide. To end the presentation (and turn off Keynote’s video output), tap the Close icon.
To highlight a particular word or image on a slide, use Keynote's simulated laser pointer.