Namu is an Japanization of the Sanskrit word "namasu," which means "devotion" and "compliance." It is often translated as " I take refuge in..."
Thus, Namu Amida Butsu would mean I take refuge (and believe) in Amida Butsu.
Namu Myoho Renge Kyo means one takes refuge in the Sutra of the Lotus of the Wonderful Law (Myoho Renge Kyo) also called the Lotus Sutra (Hoke-kyo)
Other common expressions are Namu Butsu (I take refuge in the Buddha) and Namu Sambo (I take refuge in the three treasures)
Sutras are scriptures in which are compiled teachings attributed to Siddhartha Gautama (the historical Buddha.) This teachings are split in truths as taught by him and guidelines he left for the monks and nuns. (The Sangha)
In general the doctines are refered to as sutras and the guidelines as precepts.
After the death of Siddhartha Gautama, his followers compiled the text and made extensive commentaries. All three documents, the sutras, precepts and commentaries are called the Three Stores or Three Baskets.
Like the bible, the compiling of the Sutras has a story. After the Buddha's death, Mahakasyapa, who was in charge of leading the Sangha, was afraid that the teachings would be lost or scattered.
He then gathered 500 advanced disciples and had them write down the teachings of Buddha:
He asked Ananda, who was the Buddha's constant companion, to recite all of Buddha's sermons in front of an assembly that was in charge of approving what they heard and writing it down.
In the same fashion. Upali, another disciple was put in charge of reciting the precepts.
The scriptures were also later edited and rearranged to become what we have today.
The principal sutras in Japanese Buddhism are:
At the beginning, the followers of Buddha renounced the world, left their homes and took to the woods and mountains. Lay followers, wanting to seek knowledge and teachings, asked them to take a permanent residence so that it would be easier to seek them out.
Thus were born the Shôja, the ancestors of the temples.
These small hermitages became bigger as more people came and the monks attracted followers. Those became monasteries or temples with some branch temples when the temples started organizing in sects (or schools) according to the teaching they were following.
A Pagoda is a multi-storied tower. Early Buddhists did not build graves for the deceased as the believed in the continuation of life through reincarnation. Holy men who attained Nirvana though, were not reborn. It is the case of Buddha. At his death, his body was cremated and the ashes split in 10 urns. Each urn went to a different country. In these countries, they started building Stupas (sotoba in Japanese) to venerate the Buddha.
These stupas were shaped like a bowl upside-down. With time, and geographical influence, they changed shape so much that when reaching Japan, they took the common five-storied tower we see at major temples in Japan.
In Japan, influence from Taoism, there are the five elements; earth, fire, water, wood and air. each story of the pagoda represents an element.
It is not uncommon to put the ashes of important priests in these towers.
More Facts after the jump.