Allah, the exalted has created jinns and humans to worship him only.
[And I (Allâh) created not the jinn and mankind except that they should worship Me (Alone). – 51:56].
Jinns are created from a smokeless fire as Allah says in the Quran:
[And the jinn: He created from a smokeless flame of fire. 55:15]
Just like human beings, the jinns are from different communities (Muslims, Hinduism, Christians, Jews, etc…) and behave differently. Some are obedient towards Allah while some work for magicians. Among some of the ranks of the jinns are: Ifreet, Maarid (the strong ones).
Some can fly and are very quick in reaching their destinations as Allah says in the quran:
[A ‘Ifrît (strong one) from the jinn said: “I will bring it to you before you rise from your place (council). And verily, I am indeed strong, and trustworthy for such work.” – 27:39]
The maarids are very strong and many among them try to ascend to the heavens to steal information which are being discussed and get pushed away by pelted fire as Allah says in Surah Swaffat (37)
[And to guard against every rebellious devil. – 37:7 ]. This phenomenon is the cause of the falling stars which some interpret as “Make a wish and you shall be granted”
There are other jinns which leave in the sea who dive and are known as “Ghawwas” as Allah, the exalted says in the Quran:
[And also the Shayâtîn (devils) from the jinn (including) every kind of builder and diver, – 38:37]
There is no doubt that not believing in the existence of jinns is disbelief as Allah, the exalted has already talked about them in the glorious Quran and not believing in the quranic verses is kufr and the punishment is a painful one as Allah says:
[Surely! Those who disbelieved in Our Ayât (proofs, evidence, verses, lessons, signs, revelations, etc.), We shall burn them in Fire. As often as their skins are roasted through, We shall change them for other skins that they may taste the punishment. Truly, Allâh is Ever Most Powerful, All-Wise. – 4:56]