Question Ram

what should i do ?
Nothing, be happy :)

That's the way it's supposed to be—my PC is currently using 35% of my 16GB with 4 apps open plus various normal background processes—security, schedulers etc—and ~15 browser tabs.

16GB is loads of RAM for almost all users, you can relax knowing RAM won't bottleneck your system anytime soon. An advantage of having extra RAM is it reduces 'swapping', where Windows 'swaps' data out of RAM into your HD 'swapfile', which can slow operations quite a bit.