The mirror command
is very useful for creating a mirror copy of one or more objects relative to an axis to be determined.
After you click the tool, you must select the objects to "mirror", you select one or more items and then you press "enter" key or the right mouse button to confirm them.
At this point it appears on the command line 'select first point of mirror line'.
You must indicate two points which determine the axis under which the objects will be mirrored, these points can be selected on objects already drawn (using snap features) or randomly on the area of the screen, so orthogonal or not .
After selecting the second point, we are asked "erase source objects?".
In this case we will respond by typing on the keyboard "y" or "n" (which stand for Yes or Not), then press 'enter', the mirror is executed and the command is completed.
According to the choice we made, will run the mirror to keep or delete the selected items first.
You do not have that choice every time, Autocad has set the default "n" that keeps the source objects, and in any case remember your last choice and it shows on the command line, so it got to this point, most of times, just press Enter to confirm the setting already there.