Torture is a delicate subject, even abstracted in the context of a roleplaying game. You can roll a few dice against the victim's willpower or other appropriate stat, and perhaps inflict a few hit points of damage, and be done with it that way without getting into any gory details. But unless your gaming group is both mature and expressly willing to contemplate the darker side of human nature, it's better in a game context to simply avoid the question altogether and have even the most heinous villains not resort to torture. Honestly, nobody's going to complain about their PCs not being tortured!

Transcript

Han: Wait, What are you doing? You're not actually going to torture me, are you?
Darth Vader: You will tell me where Starkiller is.
Han: And then you'll stop torturing me?
Darth Vader: No.
Han: But that's not how this works!
{cut to Lando and Boba outside}
Han: Aaargh!! He's in the Dagger Bar! On Dagobah!
Lando: Look, I can understand wanting to hurt Freddo, but this is a bit much.
Boba Fett: When Vader is done, I shall have my turn. I shall wring the location of Kenobi from him, then claim my pound of flesh.
Lando: What?
Boba Fett: I need to restore my shapeshifting ability.
Lando: You mean...
Boba Fett: Yes. A transplanch operation.