On the rear of the drive casing you will see a narrow horizontal opening with two rows of small metal pins. The jumper itself is a small plactic cap that covers two of them in a vertical direction. There are three main positions before the two rows recede into an inaccessible area that you are not going to worry about. The MA, CS, and SL or SA postitions represent master, cable select, and slave.
If you are plugging in the end connector on the second ide cable the MA or master position is used. For adding onto a cable with a drive mastered already you would set it the SL or SA for slave. Optical drives are generally restricted to the master or slave positions depending on the position of the cable they are on.
With hard drives depending on the make of the main board or system they use the cable select(CS, CA) position if they are not seen with the master or slave setting. For working with drive optical and other the 4'in'1 phillips/flat head set or precision drivers can help avoid stripping the heads on the mounting screws. To extract the one there a tiny flat head may be able to loosen that up for extraction by turning with a small pair of pliers. You will want to match a replacement with the same thread and length. Usually the packet that comes with a drive is set aside here for spares.