TABLE OF CONTENTS Here are the rules:
You have to be in Paper Space (layout tab) and at least one viewport must have been created.
You have to be inside a Viewport to manipulate the scale or position of the drawing that you see in that Viewport.
At the bottom middle of the screen on the status bar there is a button that either says Model or Paper. This button displays which space you are in currently. 
When the button is PAPER you are working on the Paper sheet that is in front of Model Space. (Refer to the illustration on page 25-5)
You may cut a viewport, draw border, title block and place notes.
If you want to reach into a viewport to manipulate the display, click inside of the viewport frame. Only one viewport can be activated at one time. The active viewport is indicated by a heavier viewport frame. (Refer to the illustration on the previous page. The viewport displaying the doors is active). Also, the Paper button changed to Model. 
While you are inside a viewport you may manipulate the scale and position of the drawing displayed. To return to the Paper surface click on the word Model and it will change to Paper 
You may now work on the paper surface.
Note: Do not confuse the Model / Layout tabs
