Difference between 60hz and 120hz

[xdagex]

So I was watching Youtube video and noticed a person running a game at 45fps on the 1080p60fps option on Youtube and it looked much smoother than me playing 45fps on the same game and it looks choppy and slow, is it because I was watching on the 1080p60fps option on youtube? I have a 60hz monitor and currently have a 7870 but a GTX 970 is being delivered to my house, should I upgrade my monitor to 120hz? Would that make 45fps seem smoother on a 120hz monitor than a 60hz monitor?

And if someone could explain to me the difference between a 120hz monitor and a 60 hz monitor that would be awesome! I was thinking that If I were to buy a 120hz monitor, I would use my 60hz monitor to dual screen but I don't know if I can use a 120hz and 60hz monitor at the same time, I do not know if there will be any compatibility issues and I don't know if it would use more wattage?

 

[boosted1g]

hz is a measure of samples per second, so 120hz tv refreshes the screen at 120x a second.
This does make a noticeable difference in smoothness. Hence why there is 144hz monitors now.

 

[xdagex]

hz is a measure of samples per second, so 120hz tv refreshes the screen at 120x a second.
This does make a noticeable difference in smoothness. Hence why there is 144hz monitors now.

But the reason for me seeing the choppyness and some what screen tears at 45 fps when the other guy on Youtube runs 45 fps and it looks almost like 60fps, Is it because I have a 60hz monitor and he could possibly have a 120hz or is this a video card/hardware issue I have?

 

[boosted1g]

a 7870 is only a R7 265 or GTX 660 equivalent so it could just easily be the GPU as a 265/7870 is not going to do 1080p that well.

So upgrading to the 970 will be a large step up.
Is your power supply good enough to handle the 970?

 

[xdagex]

a 7870 is only a R7 265 or GTX 660 equivalent so it could just easily be the GPU as a 265/7870 is not going to do 1080p that well.

So upgrading to the 970 will be a large step up.
Is your power supply good enough to handle the 970?

Yeah, I have a 500W but my entire system uses up approximately 300W including the 970 and I will upgrade my PSU soon as well because I'm thinking of a SLI maybe, but I usually have no problem running 1080p as the card itself is set up for 1080p gaming, but I was just wondering that since the 970 is such a big gap between the 2 cards, will I get any stuttering because my monitor can't refresh fast enough for my 970?