What do "namu Amida butsu" and "namu myoho renge kyo" mean?

Namu means "to obey and worship a superior existence such as gods and the Buddha."
Therefore, when one prays "Namu Amida butsu," one savs "I worship Amida Buddha and follow his doctrine."
This prayer is used in many sects of Buddhism.
On the other hand "Namu myoho renge kyo" means "l obey myoho renge kyo(the sutra), and observe its doctrine," which is used in the Nichiren sect.