It's incredibly similar to Dungeons and Dragons, if you're more familiar with that. The players all have a character, with a set of stats, abilities and characteristics written on their sheet in front of them. Actions are decided either by rolling dice or by roleplaying your character. One person is the Game Master, who tells the story and controls the world that the game takes place in, including NPCs and enemies.
It offers all the fun of RPG videogames, but with a lot more flexibility and social interaction. Instead of using what the game offers, you have a lot of freedom to try and innovate to overcome challenges. It's definitely worth trying at least once.