First you need to enable viewing your cloud content on your iPad. This is done from the Settings app. Go to:
Settings.app > iTunes & App Store and under the
Show All section make sure
Videos is set to green.
Now go to the
Videos app on your iPad and you'll be able to see all your cloud-based video content you've purchased.
To download a movie or show for offline viewing, tap the icon for the show and on the show detail screen, in the upper right hand corner, is a little cloud icon with an arrow pointing down in it. Like this:
Press that button and, assuming you have enough free space on your iPad, the video will download and be available to you to view when the iPad is in airplane mode.