The AI (Artificial Intelligence) are the red icons on the world map. They are not other human players like you, but instead game controlled opponents. The AI will act in predictable ways, cannot repair their castles, and while they may pillage or ransack you, they will not destroy your village completely.
When you first begin on a new world, your village will be protected by "Peacetime" which protects from attacks made by other players, but not from attacks made by the AI! Always be sure to have some defenses built in your castle right away!