Just double tap and hold, then drag the item to the dock. Note that no more than four items can be placed on the dock, so you first have to drag the one you don't want out of it.
First go to the page wheir the item is located once you have located the item then double tap and hold on the item until you here vo say moving and then the name of the app then move it to the doc.
Concerning moving applications. You can just double tap and hold on the item until it says editing. Once it says that Drag it down to whatever position you want in the dock. If you pause in the dock wherever you are voice over should tell you what position you're in. If you would like a demonstration please visit the following link.
http://youtu.be/bjZCtC5VIdE
Comments
Just double tap and hold,
moving items to the doc
Moving applications to and from the doc