It's depend on what you mean as modding: UI or something else. For UI if you didn't worked with HTML/JavaScript before I would recommend to start with reading some tutorials on web technologies first as it's what used by PA UI.
you came to ask about this at a perfect time! Bgolus (uber dev) just made a google doc about everything with effects. https://forums.uberent.com/threads/particle-system-guide.67428/ If you want to actually know details or how to actually get the mod into the game, post here. I was asking this same question a few months ago, i could pull the thread up
I can also recommend looking through raevn's (admittedly slightly patchy) guide on this forum if you haven't done so already - here. I'm trying to make a unit at the moment and I think that is probably a good vessel to learn how things fit together.