What is Al-Fa'l in Islam? What are the causes of using charms, fortune telling and magic among people?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Al Fal (good omen) is any action or word that brings glad tidings to the person. For example, a man is sick and he hears somebody saying: 'O! Saalem' (the safe), or a man has lost something and he hears a person saying: 'O Wajeed' (the finder). Then such a person says: 'I have taken this as Fal' favorable sign and he feels that he will get cured from his sickness or that he will find what he has lost.
al-Tirmizi reported in a Hadith (he considered sound) that "the Prophet (Sallallahu Alaihi wa Sallam) when he went for some needs liked to hear: 'O Najeeh (the successful!) O Rashid! (The wise)" .
This type of Fal is likeable in Sharia. The author of "Fath al-Majeed" says: 'The Prophet (Sallallahu Alaihi wa Sallam) liked Fal (good omen) because if people hope to get benefit from Allah and if they await Allah's Help in all matters, that means they are on the good path' . But if they sever their hope from Allah then this is a devilish act'. From Fath al-Majeed pp: 268.
As for why some people use magic and incantations, the reasons are numerous. The first reason is that their hearts are not completely clean from polytheism and they hand their hearts to creatures rather than to the Creator. They do not purify their hearts with true monotheism and true belief. Also, some people are simple minded - and naif, they accept such superstitutions and are convinced by them; they even advertise them. Finally, the fact that the people who perform such misdeeds are left to act as they wish without control has made this phenomenon very common.
Allah knows best.