Sometimes a user needs to use hardware which is not built into the computer or directly connected to the CPU, these pieces of hardware are referred to as Peripherals. One function of the Operating System is to allow these devices to communicate with the CPU and interface with software.
Peripheral devices include:
These devices "speak a different langauge" to the CPU, therefore in order to allow hardware and peripherals to be controlled by the computer we need additional software called drivers. Drivers allow the CPU to communicate with the additional hardware.
Drivers are specific to different Operating Systems (a driver for Windows would not work with macOS) and sometimes even between versions of operating systems.
Some drivers get updated to allow the hardware to run more effectively and to fix bugs – this is common for graphic cards.