There are several uses of RAM when running. Some systems have shared memory for video system. That might be not very much. Then the operating system (Windows something?) will use the RAM to get started.
After that, programs you use will start taking memory to run. More programs, more is used. Pages of Internet view are usually in a hard disk file, but some more recent views might be in RAM for quick access.
As you see, there is a great variety of amounts of RAM used, depending on the hardware, the software, and the operator's activities. There is no set amount which is "right". If the hardware memory like RAM chips starts to get overloaded, then Microsnot's Windows will start sending pages of memory to the hard disk as a way to keep things going. But a hard disk is about 100 times slower than RAM. Some systems have an SSD that is almost as fast as RAM, some have a hybrid drive that is both hard disk and SSD.