The CPU usage tells the percentage of time that the processor has spent on specific applications, including Windows functions. Even when the CPU usage is at 0 percent, the CPU is constantly performing low-level tasks, such as responding to the keyboard and mouse movements.
RAM is found in modules that are plugged into the computer's motherboard. Each open application takes up a certain amount of RAM. This is not storage memory, but simply the memory required to actually run the programs. RAM is probably the easiest part of a computer to upgrade when seeking to improve computer performance.
The CPU is the component that moves files to and from the RAM as they are utilized. The CPU is responsible for the actual management of the files, whereas RAM is simply the place the files are temporarily placed.