The religion of Islam arose in the early 7th century C.E in Mecca. (Present day Saudi Arabia) It was developed from Judo-Christian traditions with the cultural views of the Bedouin Tribes of Arabia. The followers of Islam believe that Muhammad is the Holy Prophet and was sent by God to restore Islam. Followers are expected to practice the "Five Pillars of Islam" their whole lives so they can prioritize their faith and devotion over anything else in their life.
Islam, like any other religion, is an umbrella term for Muslims. The main branches of Islam are Sunni and Shiite. In many parts of the world, like Sub Sahara Africa, Sunnis and Shiites have many conflicts for land, food, and water. Each branch interprets the Quran differently and has different views on who should have ruled after Muhammad died. This has caused a 1,400 year split and forever changed Islam.
The Lunar Cndar was taken from Judaism, and uses the moons orbit to decide when a month ends or begins, when the new year starts, and when religious holidays like Ramadan, Eid Al-Fitr, and Eid Al-Adha.