How do I add a second HD

Connect second harddisk as slave as you mentioned using the jumper setting from the manual or on the harddisk. Make sure the master harddisk jumper setting for "Master with Slave present " . Connect the power supply cable. Most of the computer operating system's would detect the new harddisk once pluged in. If the new harddisk needs formatting before use format it before you can use it. To format the new harddisk right click the new drive letter form "My computer " window and click format. Select appropriate type for the formatting new harddisk. You can access the new drive now to store you files.

Turn the machine off
Open the case
Look to see if there are IDE connector (Wide Flat cable with a connector usually grey)
If this is not present look for a SATA connector usually a small red or blue wire similar to a cat5e network cable
Scew your HDD in place in the rack connect the cable either IDE or SATA
If you have an IDE drive look for a 4 pin female connector from the power supply
If you have a SATA drive look for the connector from the power supply
Once all is connected then reboot you computer typically your bios should auto detect it.

Let me know what happens from here