The Jinn are beings created with free will, living on earth in a world parallel to mankind. They are physically invisible from man and this is the reason why some people have denied their existence. The origins of the Jinn can be traced from the Qur'an and the Sunnah.
Allah, the Exalted, says: "Indeed We created man from dried clay of black smooth mud. And We created the Jinn before that from the smokeless flame of fire." Qur'an 15:26-27
Thus the Jinn were created before man. As for their physical origin, then the Prophet (Peace Be Upon Him) has confirmed the above verse when he said: "The Angels were created from light and the Jinn from somokeless fire." (Saheeh Muslim).
It is this description of the Jinn which tells us so much about them. Because they were created from fire, their nature has generally been fiery and thus their relationship with man has been upon this. Like humans, they too are required to worship God and follow Islam. Their purpose in life is exaclty the same as ours.
Allah, the Exalted, says: "I did not create the Jinn and mankind except to worship Me." Qur'an 51:56
Jinn can thus be Muslims or non-Muslims. However; due to their fiery nature the majority of them are non-Muslims. All these non-Muslim Jinns form a part of the army of famous Jinn, Satan. Consequently, these disbelieving Jinn are also called devils. Jinn also become Muslims, as they did in the time of the Prophet when a group of them were amazed by the recitation of the Qur'an. God orders the Prophet to tell the people of this event.
Allah, the Exalted, says: "Say (O Muhammad): It has been revealed to me that a group of Jinn listened and said: 'Indeed we have heard a marvelous Qur'an. It quides unto righeousness so we have believed in it, and we will never make partners with our lord'." Qur'an 72:1-2
In many aspects of their world, the Jinn are very similar to us. They eat and drink, they marry, have children and they die. The life span, however, is far greater than ours. Like us, they will also be subject to Final Reckoning by God the Most High. They will be present with mankind on the Day of Judgement and will enter to Paradise or Hell. God has given the Jinn powers as a test for them. If they oppress others with them, then they will be held accountable. By knowing of their powers, we can often make sense of much of the mysteries which go on around us. One of the powers of the Jinn is that they are able to take on any physical form they like. Thus, they can appear as humans, animals, trees and anything else. The ability to possess and take over the minds and bodies of other creatures is also a power which the Jinn have utilized greatly over centuries. This however, is something which has been prohibited to them as it is a great oppression to possess another beings.