Linux is an operating system much like Windows or MacOS.
While Linux does similar tasks to windows, its back end is codded differently. One such example is in windows, where you can click to install most things, Linux needs you to use a terminal prompt (on most versions).
Short answer, Linux makes it so the computer works more efficiently and for longer.
Long answer
Windows version from 7 back typically require an activation key, at first they work like normal. Over time without the software being activated the windows system will degrade. Eventually quite literally turning the machine into nothing more than a glorified paper weight. This is where Linux comes in, Linux is made by thousands of people all across the world...FOR FREE! Most common versions of Linux do not require users to make any purchases. By installing Linux on machines that need, it I am confident that the end user will receive more than a paper weight.
I'm confident all computers sent out can preform the basic tasks (reliably power on & run an office suite of software).