Coupons are sent every once and a while via our mailing lists, which you can subscribe to here.

https://www.stardock.com/

Cards are just collectibles you can receive for playing most games. Their distribution isn't uniform: some games you'll need to play for a while as single cards are handed out per hour or so. Other cards you appear to receive fairly immediately.

Each card is part of a set, you woo't be given the full set, that you can then trade others for or simply buy the rest yourself. Each card tends to be 'round ten cents. The purpose of the sets (and I went a li'l crazy with five dollars) is to get them, turn them in and receive nifty items in return. Background screens for your profile, personalized emotes, other collectibles. Also, I've received two coupons for games.

The cards/sets are nothing more than bragging rights, really.

Also, I purchased Rebellion at full price (you're welcome, Stardock). It's sorta-kinda worth it. 'Ish.

I need stop playing the huge and vast maps. It'll probably make the end game more exciting.

I have. After initially getting raped from playing timid AI's I began ownin' 'em. It makes the first half more energetic, though.

I've recently noticed the different win scenarios. I'm hoping the Mysterious Planet one will create awesome battles.

The easiest way to get a coupon might be to post on Steam's Rebellion forum. You get steam trading cards by playing eligible games, the goal being to trade cards so you can get the game's entire set of cards. With all the cards you can craft a steam badge, which among other things gives you some game related rewards (icons, artwork etc.) as well as a coupon for some other random steam game.

What often happens is that people get coupons for games they don't want, and as these coupons expire after a few weeks they have an incentive to trade them quickly for something that won't expire, like more trading cards. Many people will accept any steam trading card in return for a coupon. If you don't have any of your own yet, you can buy most of them for a couple cents on the steam market place.