I understand. But how do the signaling molecules know where they are in the body? The human starts as a single cell then keeps dividing. Somewhere, cells start to specialize. How does a cell know to become a liver cell, or nerve cell etc?
Why are the appropriate gene expressions happening where they’re suppose to?
Probably a dumb question but the idea fascinates me to no end.
Not a dumb question at all. It is one of the major issues of developmental biology: how cells differentiate. An undifferentiated stem cell is obviously receiving information — signals — from the outside that tells it what type of cell to turn into. But it is such a big topic that I can tell you little here in a comment. You can get the highlights in this fairly well-written Wiki article:
https://en.wikipedia.org/wiki/Cellular_differentiation