It's by and large mathematical software, like all renderers. So it isn't interactive in a manner like software that allows moving a character model and sequencing frames to make an animation. It's a kind of a 'kernel' in some sense for animation and 3D modelling software.

The source files contain the algorithms/computations needed to solve various equations that people involved in Computer Graphics research have came up with to simulate various physical phenomena (lighting, shadows, water, smoke, waves) in the most efficient (fast) and photorealistic sense for a single image (static scene).

Since there are various different techniques for the simulation of one specific phenomenon, it's interesting to peek into the tricks used by a very large animation studio.