Imagine that you have a set of animation curves that enable a character to walk, and another set that allow the character to run. To create a smooth transition from walking to running, you can blend the walking animation with the running animation for perhaps one second.

For blended animation, you need multiple animation layers. For the walk-run example, you would need two animation layers, Layer0 containing the animation curve nodes for the walking animation, and Layer1 containing the animation curve nodes for the running animation.

Animation layers are evaluated in the order that they were added to the animation stack: Layer0, Layer1, Layer2, ... etc.

Animation layers have a Weight (the blending weight) property, which you can also animate. For example, during the walk-run transition, you would take one-second to change the weight of Layer0 (walking) from .99 to .01, and the weight of Layer1 (running) from .01 to .99.

An animation curve node normally connects one animation curve to one FBX property. But you can also use a curve node to simply override the value of an FBX property.