A jumper is a small metal connector that acts as an on/off switch and is used to alter hardware configurations.
Check this site for diagrams of hard drive jumpers - Will probably be different to what your hard drive looks like, but its the same basis.
http://www.mysuperpc.com/hdu/jumper_pins.shtml
If you know the model number of your hard drive then you could post it on the site and we could find you the proper diagram.
Right the motherboard is that BIG board at the bottom of the case, the other "cards" that come off it are the adapter cards e.g. Video Card