Device drivers are the software programs that are designed to establish communication between the hardware on your computer and the operating system on your computer. Your computer cannot perform the tasks that you ask of it without these items and you need to know that the programs must be specifically written for the exact operating system that you have.
If you have Windows XP you need programs written for it because a program written for Windows 2000 or any other Windows operating system would nine times out of ten cause your computer to crash.
If you really want to think about what these items do for you then think like the internal workings on your computer and the programs and features of your machine are all different species. If the hardware is feline and the operating systems are canine then it is likely that they could occasionally get one another to understand what they are saying because even a blind sow finds an acorn on occasion. What you would need is a translator that had the ability to communicate with both of these species. Then they could tell them what was expected of them and they could eliminate the confusion that resulted from the lack of communication.