What is SGI? And the Lotus sutra? How many types of Buddhism are there? Someone told me about SGI, Nam Myo Ho Renge Kyo. How that is derived from the Buddha. but mostly on the lotus sutra.

Can we read the lotus sutra in English online?
The main schools of Buddhism today are Theravada and Mahayana. Vajrayana or Tantric Buddhism is a part of Mahayana.

Theravada Buddhism is mostly practised in Sri Lanka, Myanmar and Thailand, but also in other countries.

Mahayana Buddhism today has the main divisions of East Asian Mahayana (including Pureland, Zen etc.) and Vajrayana (including various Tibetan sub-schools).

The article "A Comparative Study of the Schools" and the question "What teachings do all schools of Buddhism share?" can help you with regards to comparison between the schools.

Nichiren Buddhism, which is the type of Buddhism propagated by Sokka Gakkai International (SGI) is considered to be a part of Mahayana Buddhism under the Japanese Buddhism or East Asian Mahayana Buddhism branch. It was founded by Japanese Buddhist priest Nichiren (1222–1282). Details on his life can be found here. His followers believed him to be either a Bodhisattva or Buddha. The chanting of "Nam Myoho Renge Kyo" was a unique teaching and practice of this school. A brief description of Nichiren Buddhism can be found here.

These questions may also be helpful:


How is Nichiren Buddhism different from other branches of Buddhism?
What “technically” happens when we chant Nam Myoho Renge Kyo?
How to chant the mantra Nam Myoho Renge Kyo?


You can find the online English translation of the Lotus Sutra according to SGI here. Another online English translation can be found here.

The relationship between the Lotus Sutra and the Buddha's original teachings is discussed in the question "What is the basis of Lotus Sutta with respect to original Tipitaka?"