To Access Model Space

Click the Model tab in the lower-left corner of the application window.
If the Model and layout tabs are hidden, set the LAYOUTTAB system variable to 1.
If you want to access model space from within a layout viewport on a layout tab, double-click inside the layout viewport. When you are done, you can click within any other layout viewport to make it the current one, or you can double-click anywhere else in the layout to return to paper space.
Click either MODEL or PAPER on the status bar at the bottom of the application window.