Arabic is a Semitic language; other closely related Semitic languages include Amharic (Ethiopia) and Hebrew. More distantly related are languages like Berber (North Africa) as well as historic languages including Phoenician and ancient Egyptian. Kurdish is a Persian language, most closely related to other Persian languages, including Farsi.
There are a number of ethnic minorities that speak less common languages, including Turkmen, Assyrian, and Armenian. For most of these people, Arabic is also learned and is the most common language of communication between groups. English is the most commonly taught second language in the country and many educated people speak at least a minimal amount of English if they are not completely fluent.
Religion
Muslim is the official religion of Iraq as Shia Muslims make up nearly two thirds of the population and Sunnis make up most of the last third. There is about 2-3% of the population that adheres to other religions, most of whom are Christian.
Islam (the name of the religion, whose followers are called Muslims) is a monotheistic religion, whose holy book is called the Qur'an. The Qur'an is believed to be the word of God spoken through the prophet Muhammad from 609-632 CE (Common Era is preferred over AD (Anno Domini or "year of the Lord") since the Islamic world doesn't believe Jesus was the messiah). Islam believes Muhammad was the last prophet sent to earth by God, the last in a long line of prophets, which includes Moses, Abraham, and Jesus among others.