What is a driver?
Devices are the physical "parts" of your computer. They may be external like printers and monitor or internal like graphics and audio cards.
In order for your computer to be able to use these devices, it needs to know how to communicate with them. This is done by a piece of software called a device driver.
When you attach a device to your computer, you must have the correct driver installed for that device to work. For example, if you plug in a printer but the correct driver isn't available, you won't be able to use the printer. Normally, each model of device uses a driver that is not compatible with any other model.
On Linux, the drivers for most devices are installed by default, so everything should work when you plug it in. However, the drivers may need to be installed manually or may not be available at all.
In addition, some existing drivers are incomplete or partially non-functional. For example, you might find that your printer can't do double-sided printing, but is otherwise completely functional.