A-CAD COMMAND "ERASE"

ERASE :

Erase command is often used to remove one or more objects that are not needed. In addition to Erase command,you can also use the Del key on your keyboard to delete or remove the object.

I more often use the Del key to remove the object. Because more simple epic and easy.

Command: Erase
Select objects: Specify opposite corner: 

There are two ways to activate the Erase command are: 
1. by clicking on Erase in the modify toolbar icon.
2. Click the icon Erase the MODIFY command

Select objects: Specify opposite corner: after you activate the Erase command further prompted toselect objects to be removed. Then press enter or space to finish the order.