Shi'i and Sunni are the two largest branches of Islam. The official religion of Iran is Shi'ism that includes 90 percent of the population. The rift between Shi'is and Sunnis happened early in Islamic history when they disagreed on the person who should be the leader of the community. Shi'is believe that only descendants of the prophet should be leaders of society. Sunnis believe members of the community, should consult and decide on who the caliph should be. The disagreement has historically resulted in schism.
The constitution recognizes Zoroastrian, Jewish, and Christian Iranians as religious minorities and all of them are free and treated respectfully in the society.
Islam is a simple and practical religion. It has established, clear, and easily understandable beliefs and laws that any follower or student of the religion can easily understand. Islam affirms belief in a decent, civilized society. Islam also does not demand impossible goodness of its followers, but it recognizes that all human beings make mistakes and sin. No one is exempt. Islam preaches peace, mercy, justice, tolerance, equality, love, truth, forgiveness, patience, morality, sincerity and righteousness.
In Iran as an Islamic country, men and women should dress properly. There are some rules for both males and females to obey not only for dressing, but also about their behavior and manners.
For instance, Muslim women also are instructed by Allah in the Quran to wear as a minimum Hijab (head covering). At home, with her immediate family like her husband children, brothers, uncles, grandfathers and other males (family members who are forbidden to them to marry her), and with other women, a Muslim woman may take her outer garments off, and be free to beautify herself as she wants.
Although Iranian people must follow the rules but it is not the same for tourists. There are not strict and hard rules for the ones who come to visit Iran.
If you travel to Iran as a tourist, you should know that:
Males and females should cover their body completely. Full-sleeve shirts and long pants are always good choices. Women should also cover their hair with a scarf or a shawl. Needless to say that Iranian are very kind and would consider the tourists situation and culture, so there is nothing to be worried about. Just enjoy your trip as much as you can.