In the name of Allah the Most Beneficent and Merciful.
Jinns are a creation of Allah and are fact. To disbelieve in them is to reject the words of Allah and therefore kufr.
Allah has revealed a whole chapter (Surah Jinn) and also many verses about them. They are made of fire and can change forms. There are believers and disbelievers and good and evil. To protect yourself from the evil ones then one should pray Ayatul Qursi.
Of course Allah knows best
[Answer provided by: Muhammad Salim Ghisa]