Programs need more than physical resources to get the job done. Computers rely upon collections of data called files. These files must follow a specific set of rules so that the computer can make use of them. These rules govern file naming and storage practices. We call the overall set of rules a file management system or simply a file manager.
Different operating systems have different approaches to file management. You can also install additional file management software on most computers. But deep down, the operating system has to keep track of where files are so that software will run on your computer. That way, when a program asks for a file, the operating system knows exactly where to go to get the information.
Without file management, the digital information inside your computer would be a useless jumble of data. It's like piling everything you own into a single room -- you've got everything you need but there's no easy way to lay your hands on any particular item at a given time. Because the operating system follows the rules, we don't have to worry about manually allocating space on specific sections of memory for our files, and we don't have to root around in a huge mess to find what we're looking for.