As pig-headed and stubborn I can be, I do realize that at 20, there's a lot I don't know. And there's a lot I don't know I don't know. I found a great resource on how to adult, How To Grow The Fuck Up. This website evolved from a Tumblr and now has essentially a master list on how to do adult things. This list has tutorials on finances, personal documents, health, job hunting, and even relationships.
This isn't something you'll need every day, but bookmark it so one day when you're freaking out about what the hell jury duty is and why you were selected, you can calm down and read and learn and adult properly.
Follow How To Grow The Fuck Up on Twitter and check out their tips and you'll be a real person in no time.