Apart from human beings, Allah ta’ala has created jinnat from smokeless fire.
15 And He created Jinns from fire free of smoke:
surah rahman verse no 15
They have been made invisible to us so we cannot see them. They are visible only in some cases when Allah wishes to lift the veil before some people. The jinnat are insubstantial so they can take any sensory form they want.
Now the question arises that why have they been created? Well, Allah has created them so that they may obey him and worship him. This is mentioned in the Quran.
56 I have only created Jinns and men, that they may serve Me.
surah adh dhariyat verse no 56
The first jin had been much before the creation of Adam. This fact is also mentioned in the Quran.
26 We created man from sounding clay, from mud moulded into shape;
27 And the Jinn race, We had created before, from the fire of a scorching wind.
surah hijr verse no 26,27
Keep Me In Your Prayers