Drivers are small applications that enable hardware devices to talk to your PC's Windows operating system. Usually, you'll find a driver disk included in the box with whatever peripheral you're trying to use. In addition, most vendor's websites contain a download repository of new and archived driver files. If you've used a PC for a while you'll likely notice that device drivers in Windows need to be manually updated to keep up-to-date. Your currently installed driver version may not have the latest patches for bugs, new functionality, or updated support for new operating systems like Windows Vista. Conversely, if your scanner, video card, or other device is working well, you may choose to stick with the driver you've got. One important note though: if you're a video gamer, or have just bought a game that's performing sluggishly, you'll likely want to update your video card's drivers regularly as new games continue to push these cards to their limits.
When reviewing an installed driver's version number, you'll likely see the driver listed with a revision number, such as 1.0214, or a specific date. You need to be a little bit careful with driver editions as they usually encompass many little files, who each have their own version numbers as well. Sometimes when you download new drivers, you'll get a single executable file or a .zip archive that contains a number of individual files. With .zip files you'll need to extract all the files from the archive and then run a specific setup.exe file that contains the autorun feature of the package. To simplify the installation process vendors like ATI, NVIDIA, and Intel offer a one-file-fits-all solution to update all of the various editions of hardware they have in the marketplace.
If a peripheral or a component you are trying to use isn't working properly a quick way to troubleshoot the problem is to look at the manufacturer's website for available driver update files. After you've got a handle on the model number and brand of the device you're trying to use head over to the Downloads or Support area of the manufacturer's site.
A side note: often devices inside your PC that are malfunctioning are directly connected to the motherboard of your computer. For these, be it sound, video, USB, or other type of device, check the mainboard's manufacturer site first to see if you can update the whole works in one go. Typically, the vendor's site will have a section with the up-to-date drivers available for download, and these usually list the version number to compare against the one you currently have installed. The lower the version number, the older the driver, so check yours against the latest version and see if you need to upgrade. If your existing driver is up-to-date but corrupted it still may make sense to overwrite the version you have with the one you download to repair the issue.