Hi! I’m creating a game and one of my core mechanics is a special rouge like upgrade system. I Have no clue how to do this and would like to be pointed in the general direction to start. The general idea is to take the extensions icon
and create a modular expansion system so that you can drag and drop the upgrades to where they connect with each other forming a unique skill tree. depending on the rarity of the upgrade, the upgrade should have 1-4 pits/indentations, which drag and drop to connect with their corisponding counterpart. If you could give me a basis on how to do this at all, it would be SO much help. thanks! P.S. Sorry if the photo didn’t show it said I could drag and drop or copy-paste so I did. if you need a better example I can probably find one, or you can just look near the top right corner of you computer 
I recommend you start with a drag-and-drop tutorial. Then build on that. Once you have that and have some code, you can post it and say “this is what I have - this is what I’m trying to do.”
The puzzle pieces are a bit unclear, but I’d recommend you make the graphics for them, and then add them as Sprite2Ds, each with its own scene, and each scene can say which other puzzle pieces they fit with. But if you want more specific help, you need to sit down and design exactly what you want it to look like.