In its most simplistic usage, it can set the animation keys of a parameter by applying the mesh, modified or not from the Get Parm Keys Node.
However, it is also possible to create keyframes from scratch. All you have to do, is provide points, whose x positions represent the keyframe value in frames, ie. x = 1 represents a keyframe at frame 1, x=2 represents a keyframe at frame 2, and so on, and the y value will be the value of the keyframe at that time. Furthermore, a parm attribute is required, in which you specify the full path to the parameter of the keyframe, ie. /obj/null1/tx for the translation of a null locator.
Additionally, when setting the keys, you can choose to reduce the keyframes at that time.
Video Demonstration.