How do nodes work?

I’m trying to learn how to composite within blender in the node compositor. And cannot find any decent tutorials or any reading material on how nodes work? I come from after effects way of thinking.

Basic foundational knowledge is all I’m looking for in this question.

How do nodes work ?

Nodes work in the line of thinking like this:
I take this image and then I do this and then I do that and so on. And then I take another image and do this with it and then I combine the the two together and in the end I write them out to some file.

Nodes construct a network of operations that follow each other, so you should get used to thinking, what exactly do you want to achieve and in what order should you do things to get there.

Internally, the mechanics of compositing work the same, be it layer or node based. Difference is in visual representation for the artist.

I would only add that Layer systems require you to duplicate an image to re-use on another layer.
In Nodes you simply grab another node connection line and plug it in elsewhere, bang, instant duplication.

Nodes appear in many different contexts within Blender now, and I like to think of them as “a data production-line.” Data flows into the network (affectionately called a “noodle”), from one or more node-types that are “inputs,” and eventually it flows out through a node-type that is an “output.” In between are the nodes that act as filters of some kind. Data flows in, and eventually flows out again.

The inputs to a node are on the left; the outputs, on the right. Each connector is color-coded to indicate what kind of data it wil produce or accept. The colors must match.

You can now “run hoses” between outputs and subsequent inputs, describing the way that the data is to flow. You set parameters on each node to control its operation.

To keep your diagram clean, you can also create node groups, which are collections of nodes that can act as a single node. (In computer-jargon, we’d call that a macro.) You can “expand” the node group to see what’s inside. And, you can duplicate the groups.

It’s important to see nodes as a creative tool. And, as a form of visual computer programming, which in fact it is. (One node-type allows you to use Python.) As long as you wire up the noodle “legally,” that is to say properly matching the colors, you can do anything. Nodes encourage experimentation.

A beginner tutorial about nodes and how it works : https://www.youtube.com/watch?v=fWcCkQ3943Y