What the heck is a F curve modifier anyway?
If you open up the N-Panel (right side) in the Graph Editor, you get a Tab called Modifiers (if you have them enabled via the ‘wrench’):

Here I added a Noise Modifier to the X Location and you can see what it does.
Sometimes used to fake a handheld camera shake, but there are many more Modifiers and they all modify the curve (or a part of it) n some way.