How to get Out Of Trouble in AutoCAD

You may invoke a command and then realize that you are not using the right command for the desired task.

you can press the <Esc> key to cancel a command that is currently running
or you can right-click in the drawing area to invoke a shortcut menu & pick Cancel.
you may have to canceltwice in some situations to return back to the “Command:” prompt.

For example, if you invoke Line you could press <Esc> at the first (or any other) prompt to cancel the command at that stage.

Command: LINE↵
Specify first point: <Esc> *Cancel*
Command:

Dialogue boxes normally have a Cancel button as well.

you do not have to worry about invoking the wrong dialogue box because you can always Cancel it.
pick Cancel to close the current dialogue box without actually performing any action associated with that dialogue box.

You can undo commands if you are not satisfied with the end results of recent changes to the current drawing session.

AutoCAD will undo one command each time you invoke U  (or each time you select Undo from a right-click shortcut menu).
you can repeatedly use U to undo commands (one-at-a-time) right back to the beginning of the current drawing session.

There is also another command called Undo that is more powerful and lets you control undo features.

If you undo one too many commands you can use the Redo command to undo the last U command.

As with most Windows applications you can access on-line Help by pressing the F1 function key.

if you are not familiar with Help in other applications you should begin with Using AutoCAD Help on the Contents tab.
press F1 while a command is running for help on that command.