Arabic is the main or only official language in 15 countries. As you can see from this interactive map, the maojority of these are in the Middle East and especially the Gulf region. It is one of the official languages in a further 10 countries including Sudan, Somali and Israel. In some Middle Eastern countries, such as Morocco, Arabic is one of the two official languages (the other language of Morocco is Berber) though it may in fact be the better known or major one politically or practically. This is also true of Iraq, where the other major language is Kurdish.
Arabic is also widely learned, read and spoken in countries where it is not an official language, due to the presence of Islam in non-Arab countries and people learning to read and recite the Koran in its original language. This is why there are many more Arabic speakers than there are residents of Arabic-speaking countries.