You
can open up flows and check them out but Fusion can be pretty obtuse to just check out. The really useful things come from people who have bent the tools to their will and use it in full productions. The flows in the Bin are OK but they are a bit archaic and the ones like the 3D reflections are broken and a spider web that takes a while to reverse engineer.
There are some great resources for learning Fusion node flows. Somebody who hasn't made anything for a bit but absolutely shows some of the best flow theory and explains the rationale behind it is Vito.
https://www.youtube.com/c/ConFusionHe goes over large project layout and workflows that use things like wireless nodes, bitmaps, and ingest regions.
Milolabs is also a great resource. He is the wildest I've watched that uses a spiderweb approach to layout. He's really good and can keep track of it but he definitely "crosses the streams", so to speak.
https://www.youtube.com/c/millolabtutsBetween these two, you should be able to see what sophisticated layouts look like.
Once you know what you're looking at, the other thing to do is watch Nuke tutorials. They all work vertical but then again, so do most of the compers that get deep into it. Top to bottom feeding in new branches from the left and mattes from the right.
After a while you'll start to use the theories and can just save out parts of flows as macros and ".setting" files to add to your tools. It's a deep rabbit hole that ends up with making custom tools for what you need, which is pretty freaking cool.
Here's an old thread where somebody was looking at how to make a planet with atmosphere. By the end, it was a pretty nice flow that could be copy and pasted.
https://forum.blackmagicdesign.com/viewtopic.php?f=22&t=181447&hilit=+fall+offYou could take most of that code and save it to a ".setting" file called "Planet3D.setting" and throw it in your macros folder. From then on, just type Planet3D into the tool window and you're done.