Did you take Course 2 in this series? That’s where TF was introduced (C2 Week 3). In Course 4, they just give some examples of new constructs as they occur. If you want more background on the Keras Sequential and Functional APIs, here’s a thread from fellow student ai_curious which is really worth a look.
There are also lots of tutorials and examples on the TensorFlow website. The only thing you need to be a bit cautious about is that we are using a version of TF that is more than a year old and things mutate pretty fast. There are ways to request a particular version of any of the TF docs. You can find the version in any of our notebooks by doing:
print(tf.__version__)