As an After Effects user, you can expect a huge shift in paradigm moving form a layered-based environment to a node-based one. But there are more things to get used to than just networks and how things are done. If you are trying to move from After Effects to Blackmagic Fusion you need to understand how the coordinate system in BMD Fusion differs from Ae. It is one of the foundational things you need to know to be able to work with Fusion expressions.
TOKYO’s Creative Director, Simon Ubsdell offers After Effects users a quick-start for working with expressions in Fusion. Expressions are useful in both Ae and Fusion, but you need to have a good undertaking of the difference for how they work in Fusion, before moving on.
This is a great tutorial for beginners, with some special tips for After Effects users to help them feel more comfortable in Fusion.