Using the Mirror command, you can make a mirror image of a drawing object in AutoCAD. To explain this command, I will use the drawing shown here:

Here, we have a door on the right side of the wall and we need to add another door on the left side of the wall with an exact distance. In the following example, we will mirror the existing door about mid-wall to get the second door using the Mirror command:

1. Select the Mirror command from the Modify panel or use its command alias, MI.

2. Now, the command line will prompt you to select the object. Click on the green door symbol to select it and press enter.
3. Now, the command line will prompt you to specify the mirroring line. This will be a reference line that the mirror image will be made around. Click on the midpoint of the wall and then again on another point right above it, as shown:

Now, the command line will prompt you to specify whether you want to erase the source object. The source object is the door symbol we used to make the mirror image. If you select Yes, the original door symbol will be erased but its mirrored copy will be retained. If you select No, both the door symbols will be retained. The default option, in this case, is No, which is shown in the angle bracket. Simply press Enter; the default value will be selected and you will get a mirror image of the door symbol:

The Mirror tool treats text and drawing objects differently and so when you mirror text, you won't get the expected result. To mirror text just like a drawing object, change the MIRRTEXT system variable to 1. The default value of the MIRRTEXT system variable is 0. After, the mirror tool lets you look at another modify tool, called offset, which helps you make a copy of a drawing at an offset distance.