About Composite Nodes
The Composite node allows you to use several images and output a single image. You can compare that to doing pre-compositions in editing software. You can connect several drawing, image generators and effect nodes in your Composite node and one bitmap (or vector in some cases) comes out of it.
Refer to the following example to connect this node.
By default, the image resulting from the Composite node is a bitmap. The layers are composited together depending on their position on the Z-axis (forward-backward) first, then their order in the Composite node. If two images are at the same position on the Z-axis, their order in the Composite will determine which one is displayed in front and which one is displayed behind.
For more information about the Composite node options in a 3D environment context, refer to About 3D Input Output Options.