Knights of the Old Republic is an epic adventure in the Star Wars universe. Over the course of the game you will experience many worlds and meet many people, and your behavior towards them will affect the course of the game. Except for the opening and closing stages of the storyline you can travel freely between the planets and visit them in any order you choose.
Dialog is a central mechanic. Many quest decisions and outcomes are chosen through dialog rather than actions, and you will be given these choices throughout the game. Your choices affect your alignment; good choices give light side points, while evil choices give dark side points. Because many Force powers gain bonuses from the strength of your alignment it is in your best interest to choose an alignment and aspire to mastery.
While there are some exceptions, choices that are kind, selfless, or honorable will earn you light side points, while choices that are selfish, aggressive, or illegal will earn you dark side points. For many decisions your party members will praise or condemn you depending on their own alignment, and the strength of their comments is a good way of judging how many alignment points the decision has earned you.