When Muhammed was in the middle of praying because of everything that was happening, when he had started praying he noticed something was in there too and when he looked he noticed that it was an angel. He opened his eyes and was scared because he had never seen an angel before, after this the angel told him to go spread God's word. When Muhammed had seen this he did not know what to do or say he was just in shock.
Muslim women or girls wear this because they want to express or show their religion. Another reason they wear this is that they do not want men to look at them for their characteristics. Another reason why she chooses to is because it makes her herself and who she is.
The spread of Islam started with a man named Muhammed. Muhammed first told his wife about this, he only told his wife this because he was scared to tell others because they would think of him as a fraud and would not believe him. When he felt more comfortable he started telling many other people. Another way it spread is by conquest, schools, etc. This caught many people's attention and they started converting to the Islamic religion.