I am not a member of SGI, but I have been to a Nichiren Shoshu temple several times and SGI's practices and philosophy are based off of Nichiren Shoshu so I'll give a bit of input. Like Nowhere said, you'll find an extreme emphasis on the Lotus Sutra and the practice of Daimoku (reciting Nam myoho renge kyo). Nichiren, the founder of Nichiren Buddhism, taught that by practicing recitation of the Daimoku, one can reach enlightenment within one's lifetime. This is because, according to Nichiren (as well as other Buddhist thinkers to some extent), all people have an innate Buddha-nature, that is, all people have the potential to become a Buddha. With the help of the Daimoku, we are able to realize this innate nature we all have.
While I appreciate some aspects of Nichiren Shoshu, I am not a huge fan. For one, they emphasize on the fact that Nichiren is a latter-day Buddha, being superior to Gotama Buddha. Another thing that bothered me, was, like I have heard about SGI, they seem a bit "cultish" in nature IMO.
(Sorry about answering a question in a DIR, but I felt like I needed to share my knowledge
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