Monitor hertz is frames ?

Yes, you need a 120Hz monitor for 120fps ans so on. Even if your PC is faster, your display can only do 60fps.

That said, some TVs claim to support refresh rates as high as 1000Hz, but that's only in theory. The fastest you can get is 144Hz. There are some 240Hz gaming monitors out there but they only take a 120Hz and "double" the signal so to say.

Bystander is more correct then Eduello. Monitors are based on old CRT technology, which is based out of Film standards. Film is normally 30 Frames of a single image per second, then another 30 frames, of the image changing (say lifting you hand a little higher) and so on until when you flip through all the frames in sequence you get the 'visual effect' of movement as perceived by your eye, when in fact your just seeing different 'still' pictures in sequential order. This is called the SOURCE VIDEO.

Standard TV frequencies were 60Hz, this would be incompatible with standard 30FPS, so they used a technique to 'upscale' (I believe the term is) so it matches the 60Hz signal, this is called DISPLAY VIDEO. So the film / TV / movie / game / etc. could be 60FPS, 30FPS, even 5FPS, the screen it self will always show 60Hz no matter what. When we went LCD and the potential for more HZ, like 120Hz, 240Hz or now 4KHz, they used new techniques to actually 'add' actual more FPS to the SOURCE Video by duplicating, so if you had frames 1,2, 3,4 it would make 1, 1a, 2, 2a, 3, 3a, etc. then keep duplicating till it matched up tot he Hz frequency. Again though the source (what happens in the game) can still be only 5FPS or 1000FPS, it doesn't matter, it just needs to 'match' the frequency is all the monitor and GPU cares about.

So getting a 120Hz monitor or 4K TV to display on doesn't make your 'game place' 120FPS or 4000FPS (remember the human eye only perceives 60FPS anyway, the rest is lost). What it DOES do is during the 'movement' (dodging left, swinging on a vine, etc.) more 'smooth' or realistic (often referred to with disdain as the 'Soap Opera' effect as they use higher FPS video then normal broadcast TV). Also for us OLDER folks, it makes it more clearer to see your foot move in the 'bush' to avoid getting headshot, when we are talking only a few pixels young people 'twitch' to and we can't "see any difference" when we look.

What will improve the FPS of a game (if that is your goal) is a MATCHING performance across your hardware of the PC. This is a heavy investment, where your matching the speed of a storage unit (7200RPM HDD) to the speed of RAM (DDR3) to a decent CPU (i5 or i7) and the appropriate GPU that matches all up together when playing.