Using the toolbar
Each icon in the toolbar is a menu giving access to different categories of nodes (ie. image processing tools) that Natron offers to process or create images.
If you click on a tool, the corresponding node will be added to the node graph
Note
If a node is selected in the graph, the new node will be inserted below the selected one. It will be processed right after the selected one.
Image tools
The nodes to bring images in and out of Natron, plus a few utility nodes.
Draw tools
The nodes to create basic shapes.
Time tools
The nodes to change the timing of your clips.
Channels tools
The nodes to changes the order of your image channels (basic channels are RGBA for Red Green Blue Alpha but others can be added).
Colors tools
Mainly color correction nodes.
Filter tools
Nodes to change the texture of the image (blur or sharpen for example).
Merge tools
Nodes with multiple inputs that can merge multiple images into one composite image.
Transform tools
Nodes to change the geometry of the images.
Views tools
Nodes to manage stereo images that considered as different views (left and right).
Other tools
Mainly utility nodes to keep the node graph clean and readable.
Note
Other entrys in the toolbar can be added with plugins / scripts. So your Natron installation may have other Tool icons (community plugins,…)