Nodes are the building blocks of the scene. The Houdini scene is built from nodes organized in networks. Different network types control different parts of Houdini.
Using the shelf tools automatically creates nodes. For example, when you click the 
Box tool on the Create shelf tab, Houdini creates a new 
Geometry container object with a Box node inside. You can also create nodes manually in the network editor. This is how advanced work is often done in Houdini. Pressing ⇥ Tab in the network editor opens a menu of all nodes available in the current network type.
Some nodes can contain other nodes. For example, a Geometry Container object node lives at the scene level. It contains a network of surface nodes that define the geometry of the object. See node navigation for information on how you move inside and out of container nodes.
Each node in a network performs a specific function. In geometry, compositing, and CHOP networks, each node creates or modifies data passing through the node. At the scene level, nodes represent objects (such as props, bones, lights, and cameras) with transforms and parenting relationships. In the render network, nodes represent rendered outputs (images or animation), and links between the nodes define render dependencies.
Subtopics
Networks
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How to create, move, copy, and edit nodes.
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How to move around the networks and move between networks.
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How to connect nodes to each other to make them work together.
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Flags represent some state information on the node, such as which node represents the output of the network. Different network types have different flags.
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Badges indicate some status information about a node. They usually appear as a row of icons below the name of the node.
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How to use the Find dialog to find nodes based on various criteria.
Editing parameters
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How to change the behavior of nodes by changing their parameters.
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Explains the tricks to working with ramp parameters.
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Pattern matching in parameters
An explanation of the special characters available in pattern-matching parameters.
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How to change the parameter interface of a node.
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How to create references between parameters and create node copies that reference the original.
Next steps
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How to automatically clean up, align, and distribute nodes.
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Organizing, customizing, and annotating nodes and networks
How to keep your networks neat and well documented.
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Every node and parameter has a unique pathname you can use to refer to it.
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How to display lines and indicators representing channels references between nodes.
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Guide to network editor options.
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A quick reference for hotkeys and user interface shortcuts in the network editor.
Expressions
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You can enter expressions into a parameter so its value is computed instead of being static or keyframe animated.
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How to use variables and expressions in file path fields to generate numbered and unique filenames.
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How to add extra parameters to an individual node.
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Tips and tricks for writing expressions to accomplish various effects.
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Expression functions let you compute the value of parameters.
Guru level
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Motion Effects let you easily add secondary motion to keyframed parameters (usually translate, rotate, or scale parameters), such as jitter or overshoot.
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Custom HScript expression functions
How to add custom functions to the HScript expression language.
Reference
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Explains all the menu items in the network editor menus.
