This 2 Part step by step tutorial is suitable for absolute beginners, even if you have never touched Fusion before in your life.
I am creating a very simple sky replacement, only using the merge node and then animate the new clouds using the corner positioner.
In the second part, I am adding a title to the picture, animate it and mask out a foreground object, so that the title moves through the background.
It is possible to do much more with the same picture, but this is just meant to be a super slim composite to get you started in Blackmagicdesign Fusion.
This quick start tutorial is taken from the beginning of my full training course: Blackmagic Fusion: Your Journey from Beginner to Expert.