Hello,
Rankings are more like legions, or that's how I look at it. For every game you play, you get a certain amount of trophies. Your goal is to be in the top 5 trophy count in your division- you'll move up to the next legion. For your resignation issue..You could ask people on the forums to play you until the very end, or just play a lot more people-I've started to checkmate a few, but people still resign.

Hello, I recently got into chess.com 3 days ago, and I don't think I've ever won by checkmate here before. My opponent always resigns, and while it gives me points, I am terrible in the endgame. Is there any way I can practice someplace better? I've tried with bots, but they are a bit predictable.
Also, while you are here, can anyone explain the rules of rankings here? What are these stone, wood, and bronze division things? Also, what are the other ranking things, like rapid and blitz?