You can backtrack your recent actions using one of several methods.
Undo a Single Action
The simplest method of backtracking is to use the UNDO or U commands to undo a single action. Many commands include their own U (undo) option so that you can correct mistakes without leaving the command. When you are creating lines and polylines, for example, enter u to undo the last segment.
Undo Several Actions at Once
Use the Mark option of UNDO to mark an action as you work. You can then use the Back option of UNDO to undo all actions that occurred after the marked action. Use the Begin and End options of UNDO to define a set of actions to be treated as a group.
You can also undo several actions at once with the Undo list on the Standard toolbar.
Reverse the Effect of Undo
You can reverse the effect of a single U or UNDO command by using REDO immediately after using U or UNDO.
You can also redo several actions at once with the Redo list on the Standard toolbar.
Erase Objects
You can erase any object that you draw. If you accidentally erase the wrong object, you can use the UNDO command or the OOPS command to restore it.
Cancel a Command
You can cancel a command without completing it by pressing Esc.