1. Open a new drawing. Click New 
2. Make sure Ortho mode is ON, (it ON when it glow in blue)
click the icon to turn it ON or OFF. (or press F8 to toggle)
3. Type z [Space bar], e [Space bar]. This will zoom extents your drawing area.
4. Activate rectangle command. Click Rectangle.
5. Specify first corner point of the rectangle at 0,0. Type 0,0 [Enter].
6. Move your cursor to right side and specify other corner point at 10,6. Type 10,6 [Enter].
7. On ribbon tools, modify click Chamfer.
8. Look at command line status;
After command chamfer executed, we need to specify distance1 and distance2 of the chamfer.
9. For this autocad tutorial we will specify chamfer distance to 1 or 1@45deg chamfer. Type D and enter dist1=1 and dist2=1.
10. Click on first edge of the chamfer.
11. Click on second edge of the chamfer.
12. Press [Enter] to confirm the chamfer.
13. Repeat step 7 to 12 to chamfer other 3 edges.
14. Press [Esc] key few times to end Chamfer command.