There are four Apps in your App dock by default: Safari, Mail, Photos and iPod. Those are intended to always be within reach while navigating the iPad’s menu. You can drag more icons into that dock very easily.
Let’s say you want to put the App Store down in the dock:
1) Hold your finger on the App Store icon
2) Wait for it to to do the iOS jiggle
3) Drag it down into the dock.
4) You can have up to six icons at the bottom.