Adding a hard disk is a simple task for just about anyone; power down your system, open the case, slide the drive into an empty bay and insert the SATA cable or Ribbon Cable (red line facing the power cable), connect the power, and start the system. However, identifying your hard disk type and how many you can have could be another issue entirely...
Your system should support any capacity hard disk, so it's simply a matter of identification; the easiest route is to simply Google your motherboard version (and it should be in a huge font on your motherboard, as all manufacturers proudly want to spam their product).
If you can't find the model on the motherboard you're not at a loss, you can identify most times by the adapter; there are two main types of connector, the current standard is SATA (which, from looking at the cable, is about an inch long and has no pins), and the older IDE/ATA (which is a bulky 40 pin adapter). The SATA specification is backwards compatible, so you can buy an SATA III drive and use it on a system which only supports SATA; though you won't ever reach the speeds by using an outdated cable, or using a port on your system that doesn't support the higher standard.
If you're using a Desktop Computer you'll generally go with a 3.5" hard drive, whereas on a Laptop Computer you'd generally be going with a 2.5" hard drive. If you're looking at an SSD drive you'll be getting a 2.5" drive and will need an
SSD Mounting Bracket, which supports 2 SSD drives, in order to place the drive in a 3.5" bay on a desktop computer.
Now that we know what we're looking for, we can head over to
Amazon and look at the selection of
Standard Mechanical Hard Drives or a
SSD Hard Drives; you'll be looking at customer reviews and ratings in order to locate a reliable drive.
There are also
External Hard Drives which come with their own USB enclosure,
USB Flash Drives which just sit on an open USB port, or
Network Hard Drives which plug into your network, if you don't know what ports you have on your machine, you can usually just default to USB (as all else fails, you can just buy a USB hub if all of your ports are full).
You can also make your own external hard drive.
SATA Standards vs Speed:
SATA revision 1.0 (1.5 Gbit/s, 150 MB/s, Serial ATA-150)
SATA revision 2.0 (3 Gbit/s, 300 MB/s, Serial ATA-300)
SATA revision 3.0 (6 Gbit/s, 600 MB/s, Serial ATA-600)
SATA revision 3.2 (16 Gbit/s, 1969 MB/s)
ATA Standards vs Speed:
Original: 8.3 MB/s
Later: 33, 66, 100 and 133 MB/s
Note - As SATA III and IDE/ATA133 are backwards compatible with their predecessors, you should have no problem putting them into a system as they will be read regardless of their faster specs. However, SATA and ATA themselves are NOT the same types of drive, thus you cannot put an ATA drive into an SATA slot (it wouldn't fit in the first place).