"Nodes" are individual blocks that perform a certain operation, and might have one or many different outputs.
Conceptually, there are three basic types of nodes:
- Input Nodes
- these nodes produce information, but do not have any inputs of their own.
- Examples are: Render Layers, Value and RGB nodes.
- Processing Nodes:
- these nodes filter or transform their inputs, to produce one or more outputs.
- Examples are: RGB Curves, Defocus,' and Vector Blur nodes.
- Output Nodes:
- these nodes consume their inputs to produce some kind of meaningful result.
- Examples are: Composite node (which determines the final output used by Blender), Viewer (which displays the output of a socket), and File Output node.
The essential idea of nodes is that you can create an arbitrarily-complex network of nodes, by connecting the outputs of one or more nodes to the inputs of one or more other nodes. Then, you can set appropriate parameters (as you see fit) for each node.
This network is called a "noodle" and it describes how information literally flows through to produce whatever result you want.
You can define node groups, and use those groups as they were a single node.
You can link and append these node groups from other files.