Below I provide a short introduction to some of the world's major religions. Two of the largest are Christianity and Islam. After that, Buddhism can be found throughout Asia, Confucianism plays a huge role in Chinese culture while Hinduism permeates the India (home of 1.4 billion people).
Based on the teachings of Buddha who lived just before Socrates, ca. 500 BC. He left his family to go mediate in the mountains and came to understand existence and a cycle of life and death, the main point all of it was suffering which could be escaped by attaining nirvana. Buddha returned to society and offered his knowledge for any who cared to attain a state of peace and tranquility. The Dalai Lama is revered as the leader of Buddhists, but much of Buddhism involves personal reflection, meditation and tolerance for other people's beliefs and customs regardless of any leader. You'll find Buddhism mostly in Thailand, but it's prominent throughout the southeast Asian region. Major holidays include Buddha's birthday which falls sometimes in March. There are several denomination of Buddhism, including Theravada, Mahayana and Vajrayana.
Based on the teachings of Jesus Christ, who indirectly gave us the Christian dating system (Before Christ (BC) / Anno Domini (AD)). Much of his teachings can be found in the Bible which was written by his disciples, from whom the Pope derives his lineage. Jesus was crucified at the age of 33 on charges of blasphemy (after all, he was telling people he was the Son of God, which some people didn't like too much). If you choose to go to the Philippines, or are perhaps in the area, it's one of the most religious countries in the world. If you're there for Easter you may want to witness the Good Friday crucifixions, where devote followers of Christ choose to be nailed to a cross for a short period of time. Aside from the Philippines, Brazil is the most Catholic country in the world and hosts the statue of The Redeemer. Christians fall into one of many denominations such as Protestants, Anglicans, Catholics, and others. Major holidays include Easter (in the spring, usually in March or April) and Christmas (on December 25thevery year).
Based on the teachings of Mohammed who lived around 600 AD and preserved in the Quran. Though most people will associate Islam with terrorism, the truth of the matter is that it's like any other religion with its basis on “being good” so you will be rewarded in the after life. The problem stems from what some people understand to “be good,” as that can be interpreted in any number of ways. In any event, Islam dominates the Middle East and many parts of Asia, including Malaysia, Singapore, Myanmar (Burma) and much of Indonesia. Major holidays include Ramadan, which usually takes place during July and August, but varies according to the phases of the moon. Devote Muslims will abstain from alcohol (but they'll smoke instead) and not eat pork. Further, you'll notice that Muslim women will wear a dudong, a type of headscarf, not to be confused with the burqa, a full body covering found in the Middle East. There are different denominations of Muslims, the two most prominent are the Sunnis and Shi'ites.
Though not really a religion so much as a system of belief, Confucianist beliefs walk the line between religion and spirituality. Overall, is an ethical and philosophical system based on the teachings of Confucius who lived around 600 BC. Confucius is often quoted by folks who like to read philosophical discourses, since much of his material is so quotable. However, his basic tenant was that you need to be concerned with the here and now, ie, this world and the people in it, not the gods and the afterlife. The reason for this is because humans can be taught and, in essence, progress and enable themselves to learn, grow and evolve. Confucianism will be found throughout Asia, especially in China, South Korea, and Japan.
An age-old religion that permeates Indian culture and parts of SE Asia, most notably Bali, Indonesia and Malaysia. Consisting of several layers of gods and goddesses, the essence of Hinduism lies in the manifestation of Vishnu who, above all, represents creation in its purest form. The number of gods and goddesses found in Hinduism can make your head spin, but it will enough to know that the people pride themselves on their duties to the gods, which means laying out small offerings several times during the day to their house-hold god. There are numerous holidays for Hindus and you'll be surprised by what goes on in some of them, namely Thaipusam, during which devotees pierce themselves with hooks, needles and other implements to show and test their faith. In regard to food and drink, you'll find many Indian restaurants are Halal, which means they don't serve alcohol and their food has been prepared in the appropriate fashion for Hindu believers. Dewali is celebrated by Hindus all over the world. Aside from those, there are many festivals in the Hindu calendar.