Closet Library Development is an advanced topic and requires a deep understanding of how Fluid Designer Works, so make sure you have gone through the getting started training series and the closet design series.
Once you have a good understanding of how Fluid Designer works then you need to understand how to write Python Code. Here are some good resources to learn python.
Finally, before you start this series you should also review the Product Library Development Training for Fluid. This will help you understand how to setup Eclipse and create a library from scratch.
This series references the Fluid Designer Python API several time.