When I set up my IPad Air, I didn't install Pages and Numbers. How di I go back and install them now?

Go to the App Store and download them.

Do a search in the featured tab of the App Store. When I type Pages into the search field in the upper right, Pages appears as the very first app.

Is this a new iPad?

How to get all the iWork apps, iPhoto, and iMovie for free on an eligible iPhone or iPad

http://www.imore.com/how-get-all-iwork-apps-iphoto-and-imovie-free-eligible-ipho ne-or-ipad

About Free Apple Apps for iOS 7 compatible devices

http://support.apple.com/kb/HT5913

 Cheers, Tom 😉