Answer: The advantage are as follows: Obiedience to Allah. Fullfilling the purpose of Life Happiness in this life and the hereafter Saving oneself from the Hell Fire. Love of Allah and his blessings to you, family, children, marriage, business and all your affairs. With my good wishes.
because it shapes the conduct of a muslim
The belief that Almighty Allah (God) is the Only Supreme Authority makes a Muslim dauntless, honest, and truthful.
In Islamic countries.
No.
how muslims belefs in prophets influences the daily of a muslims
There is a mix of Afrians and Arabs, they're muslim.
Mainly on their holy book, the Qur'án.
There is no god but Allah and Muhammad is the messenger of Allah
No. He is Roman Catholic and rather devout in his belief.
it will certainly lead you to the success....
NOT NECESSARILY. Belief in Allah is a necessary, but insufficient condition to be a Muslim. The primary statement of belief in Islam is the Shahaada and the Shahaada has two components: (1) There is no god but Allah AND (2) Muhammad is His Messenger. Failure to believe in Muhammad's prophecy means that the person in question is not actually a Muslim.
If you are Muslim man, then yes you can marry her on condition that she is Muslim, Christian, or Jew. If you are not a Muslim man, you can't marry the girl friend if she is Muslim unless you convert; with true belief and free will; to Islam.