That's completely normal. That's what the RAM is there... to be used by the system.
No point on having RAM available that is not been used.
While I was writing this, my system RAM usage was 7.4GB.
RAM usage fluctuates depending on tasks carry out by the OS processes and apps in your PC.
In that Task Manger window I see the CPU, disk, Ethernet and VPN using system resources and translate into RAM usage.