How to make my video look less fuzzy?

I filmed it on a Nikon D5100. How do I reduce the fuzzy 'noise' on the footage? Which setting do I change and how? Thank you so much! Points for the the most helpful answer.
Even if you can't tell me how to change the settings, maybe how I can fix it in Final Cut Pro x?

ISO is responsible for the noise, whether it is a photograph or video. So try setting the ISO to lowest level possible, ussually 100 or 50 depending on your camera

You can reduce noise, you need to be shooting at the cameras lowest ISO

To do that, you will have to control the lens aperture of the lens to get good exposures.

It is my understanding that the default video ISO setting on a dSLR is "auto" so that inexperienced videographers do not have to spend a lot of time figuring out what ISO they need when shooting interior shots, where the amount of light can vary as much as two or three stops.

When shooting from a script, you can of course, get good meter readings for each take and make the necessary adjustments in lens aperture and/or lighting to allow the scene to be shot at low ISO's reducing noise to the shadow areas of the scene.