Answer:
Islam religion started about 1432 years ago in Makkah after Prophet Muhammad (SAW) received the revelation from Allah (God) through Angel Jibril (Gabriel) while he was meditating in a cave ( Gaar-e-Hira) in a mountain called Jable-e- Noor about 5 Km east of Makkah city in Saudi Arabia.
The Holy Koran was revealed in stages and The prophet propagated and preached Islam which spread all over the world. Followers of Islam are called Muslims.
Makkah is the Holiest city for the Muslims and it has the Kaaba, the House of Allah, originally built by Adam and then rebuilt and repaired by Prophet Abraham and his son Ishmael, where pilgrims go every year for Haj.
Madina city is another place of importance in Saudi Arabia as it has the Masjid Nabi (place of worship) which was built by prophet Mohammad and is also the place where he is buried.