SameDiff is the JVM equivalent to Tensorflow and PyTorch. Use it for automatic derivation or to import pre-existing models from other frameworks.
The documentation for SameDiff is currently pretty sparse. Still, before asking questions, make sure you have read Variables in SameDiff and SameDiff operations.
There are also examples to be found at:
The examples show how to use SameDiff to import models from tensorflow and how to train your own SameDiff based models from scratch.