You can view your storyboard in two different ways, either in Grid or Slideshow mode. By default, each storyboard will display in Grid mode.
You can switch between these modes by clicking on the Slideshow icon located in the upper right toolbar.
You can also hover over any frame within your storyboard and select the Zoom icon.
If you're nimble on the keyboard and prefer shortcuts you can also switch views by pressing the (g) for Grid and (s) for Slideshow.
Bonus: Use the left and right arrow keys while in Slideshow view to navigate through your frames!