It's basically a simple test your Mac does automatically to see if your hard drive is failing. Go to "About This Mac" from the Apple Menu, click "More Info", then system report. Then, click "Serial ATA" it should give you information that looks like this:
Of course capacity and manufacturer will vary.
Hitachi HTS727575A9E362:
Capacity: 750.16 GB (750,156,374,016 bytes)
Model: Hitachi HTS727575A9E362
Revision: JF4AD0F0
Serial Number:
Native Command Queuing: Yes
Queue Depth: 32
Removable Media: No
Detachable Drive: No
BSD Name: disk0
Rotational Rate: 7200
Medium Type: Rotational
Partition Map Type: GPT (GUID Partition Table)
S.M.A.R.T. status: Verified
Volumes:
As you can see mine is smart verified.
Alternatively, you could open Disk Utility, select your disk, and then look at the bottom of the window: