In the entry-level general science book I’m (eternally) attempting to write, I’m describing the expansion of space with a “big bread model.”
Imagine that you are cooking a loaf of raisin bread. You take a piece of dough that is 4 inches long and put it in a 12-inch bread pan, and it takes one hour to bake. In that hour, the piece of dough triples in length to fill the pan. Now imagine that you measure the distance between some of the raisins before and after baking the dough. Two raisins that start off 1 inch apart will end up 3 inches apart, moving away from each other at a rate of 2 inches per hour. Two raisins that start off 2 inches apart will end up 6 inches apart, moving away from each other at a rate of 4 iph. Two raisins that start off 3 inches apart will end up 9 inches apart moving away from each other at a rate of 6 iph. And two raisins at the far ends of the dough 4 inches apart will end up 12 inches apart moving away from each other at a rate of 8 iph.
The speed at which the raisins move apart from each other depends on how much dough is between them—the more dough, the faster they move. And no matter which raisin you choose to look at, all other raisins are moving away from it in all directions from it’s own point of view.
Galaxies aren’t flying away from each other like bits of debris in an explosion—galaxies are embedded in space that is expanding—and the more space there is between two galaxies, the more expansion is going to happen, and the faster the two galaxies move apart from each other.