QUESTION - What are the jinn? How are they different from the devils or from Satan? 

Answer

The jinn are a race of beings created by Allah with free will and with accountability to Him.

They are, therefore, one of the two “great worlds” that Allah mentions in the Qur’ân: “Soon shall We settle your affairs, O both you great worlds!” [Sûrah al-Rahmân: 31]

Allah created both sets of beings with free will expressly to worship Him. Allah says: “I only created the Jinn and humanity to worship Me.” [Sûrah al-Dhâriyât: 56]

As for Satan (Shaytân in Arabic), he is Iblîs, the singular being who was created directly from fire, just like Adam was created from dust. Allah says: “And He created the jinn from a smokeless flame of fire.” [Sûrah al-Rahmân: 15]

Since he was created from fire, he has a natural tendency for anger, passion, and reprehensible behavior. He refused to prostrate before Adam as Allah had commanded him.

Allah says: “Behold! We said to the angels, "Bow down to Adam": They bowed down except Iblis. He was one of the Jinns, and he broke the Command of his Lord. Will ye then take him and his progeny as protectors rather than Me, when they are an enemy unto you? Evil would be the exchange for the wrong-doers!” [Sûrah al-Kahf: 50]

As for the term devil – or shaytân in a generic sense – it refers to all intelligent beings who choose to act in an evil and iniquitous way, regardless of whether they are form Adam’s descendents or from the descendants of Iblis.

In his book, Terms from the Qur’ân and their Definitions, al-Râghib al-Asfahânî writes:
Every rebellious being – whether from the Jinn or from humanity – is called a devil (shaytân).

Allah says: “And thus did We make for every prophet an enemy, devils from among human beings and jinn, some of them suggesting to others varnished falsehood to deceive (them), and had your Lord pleased they would not have done it, therefore leave them and that which they forge.” [Sûrah al-An`âm: 112]

And Allah knows best.