What Is the Point of the Nodes in Proof of Work?

In the early days, now there are light clients and all sorts of services around. That means you don't have to store the full blockchain on your computer. But if you happen to run a full node, this is what you're storing. And so how do you determine which one is the right one to pick? You might get two blocks that fork off from in different directions. So ultimately Bitcoin is a network of computers sending data to each other.