Imagine you're standing in a dark room holding a flashlight. Whenever you turn on the flashlight, it creates a cone-shaped beam of light that shines in all directions.
Now imagine that instead of a flashlight, you're a tiny dot in the middle of the beam of light, and that the cone of light expands out from you in every direction as time goes on. This is kind of what a light cone is!
A light cone is a way of visualizing how light (or any other type of information) travels through space and time. It's made up of two parts: the past light cone and the future light cone.
The past light cone is everything that you could possibly observe or know about the universe, based on everything that has happened up to a certain point in time. This is because the light (or other information) from any event in the past could have reached you by this point.
The future light cone, on the other hand, is everything that could possibly affect you in the future, based on everything that has happened up to a certain point in time. This is because anything that could affect you in the future would have to be within reach of the light (or information) that you could emit into the universe by that point.
So in a sense, the light cone is like a snapshot of all the things that you could possibly know or experience in the universe, given your position in space and time. And as time goes on, the cone expands outward as more events happen and more information gets sent out into the universe.
Pretty cool, huh? Just remember: past light cone = things you could know because of what's happened so far, future light cone = things that could affect you in the future based on what's happened so far, and both together = a big cone of information expanding outward through time and space!