If you played a deck building game before, you'll be able to play Star Realms right away. If this is your first deck building game, you're in for a treat! It's easy to learn how to play, it's tons of fun and nothing can beat that low price.
If you played something like Dominion before, the main difference with Star Realms is that instead of having the same kingdom throughout the game, the market changes in Star Realms (you always have 6 cards out and you replenish the market when one of the cards is bought).
It also has factions, which means that you can stack up bonuses if you play cards of the same factions. And stations, which means you have to destroy the station before you can attack the player.