OK, let me have a crack at explaining things.
Events are like a photo - it represents what happens\happened
Some events can be photo-shopped, so the event seems bigger or new things occur during the event.
For example, I travel back in time and take a photo of Vesuvius erupting. This captures the "fixed point" which is an event with huge consequences.
I then photoshop the photo to include some trees and a small cart selling apples.
I haven't changed the event, only added a few inconsequential things to it.
This is a fixed point.
A point in flux is like this, but without the erupting volcano. Therefore I can photoshop as much as I like as there are no consequences.