Sometime in the process of drawing, there are some the same object but it is opposite place. You can use Mirror command. You will do it very easy. So how do you use this command in AutoCAD? You should remember that you need to define two point or an axis to do it. Mirror of shortcut is MI
How to use Mirror command?
You can practice the steps as following:
Command: MI > enter
Select objects: You select objects that you mirror > enter
Specify first point of mirror line: click on first point
Specify second point of mirror line: click on second point
Erase source objects? [Yes/No]: N > enter
Mirror command objects
Video tutorial Mirror command in AutoCAD: