If anyone has a real desire to be a Muslim and has full conviction and strong belief that Islam is the true religion ordained by Allah then all it takes is to pronounce the testimony of faith (Shahada) i.e.
“Ash-hadu anlaa ilaha illallah, wa asha hadu anna Muhammad an abduhi wa rasuuluh.”
In English it means:
“I bear witness that there is no deity worthy to be worshiped but Allah, and I bear witness that Muhammad is His servant and messenger.”
The first part of the testimony speaks of the truth that God revealed to mankind: that there is nothing divine or worthy of being worshiped except for Almighty Allah.
“We did no send the Messenger before you without revealing to him: none has the right to be worshiped except I, therefore worship Me.” (Quran 21:25)
The second part of the testimony means that Prophet Muhammad is the servant and chosen messenger of God. This implies that one obeys and follows the commands of the Prophet. One must believe in what he has said, practice his teachings and avoid what he has forbidden. One must therefore worship God only according to his teaching alone, for all the teachings of the Prophet were in fact revelations and inspirations conveyed to him by God. What does then worship means? It means rendering sincere service; showing reverence for Allah. In a deeper shade of meaning, it implies total submission and complete obedience to Allah’s commandments both in utterances and actions, whether explicitly or implicitly and whether private or public. God says about Prophet Muhammad PBUH:
“And indeed you are upon a high standard of moral character.” (Quran 64:4)
By accepting Islam, one is actually showing repentance of the life he lived before. The sins committed before, by Allah’s mercy, are all washed away and it is as if the person is just born from the mother’s womb. He disowns all forms of polytheism and false beliefs. He should reject evil and be righteous. Such rejection of evil and being righteous is one of the requisites of the motto of Islam that is, Lailaha Illallah.
“…The only religion before Allah is Islam. Those received the scriptures differed only after knowledge had come unto them through transgression among themselves. Whoever disbelieve the revelations of Allah, then Allah is swift in calling to account.” (Quran 3:19)
The Quran further goes on to say: “If anyone desires a religion other than Islam, never will it be accepted of him; and in the Hereafter, he will be in the ranks of those who have lost (their selves in the Hellfire).” (Quran 3:85)