Clean Screen
(i) The Clean Screen button hides most interface elements such as the Ribbon, and maximizes the drawing area to focus on the current drawing.
(ii) This button is at the lower right comer of the screen.
(iii) Choose the Clean Screen button again to restore the previous display state of the screen.
 

Ortho Mode (F8)
(i) You can turn ON or OFF the Ortho Mode just by clicking on it.
(ii) If the ORTHOMODE button is chosen, you can draw lines at right angles only i.e., lines can only be drawn vertically or horizontally.
(iii) You can also use the F8 function key to turn ortho on or off.

Dynamic Input (F12)
(i) The Dynamic Input button in the status bar is used to turn the Dynamic Input on or off.
(ii) If the Dynamic Input mode is turned on, the x, y coordinates and prompts show when the cursor hairs are moved.
(iii) Using the F12 key, you can turn the Dynamic Input, on or off.

GRIDMODE (F7)
(i) If the GRID MODE button is chosen, the Display drawing grid will turn ON and the grid lines are displayed on the screen. 
(ii) The F7 function key can be used to turn the grid display on or off.

The Status Bar which is located below the command line, and docked in the lower right corner of the window is called Application Status Bar.

The Navigation Bar is displayed in the drawing area and contains navigation tools.

Recent Input
(i) AutoCAD remembers the last twenty commands and options you enter at the 'Command:' prompt, or select from a menu or toolbar.
(ii) Autodesk calls this "Recent Input."
(iii) If you prefer to see a list of the command history, right-click, and then select Recent Input from the shortcut menu.

(i) The File tab bar is located at the bottom of the Ribbon.
(ii) In the bar, all the tabs added get arranged in the sequence in which the respective drawings are created.
(iii) Using mouse you can change the sequence of tabs in the File tab bar.