There are four default apps in your dock at the bottom of the iPad screen. But you can actually add two more. As you would move any app to a new location or screen, tap and hold one of the app icons till it starts dancing. Then move it on to the dock.
The first image above has four and the second is with the two extra apps for a total of six, so easy.
"iPad Tips and Tricks : Add Two More Apps in Dock "
Reference : top-ipad-video-converter.com