To convert to Islam and become a Muslim a person needs to pronounce the testimony with conviction and understanding its meaning:
Just say : I testify “La ilah illa Allah, Muhammad rasoolu Allah.”
The translation of which is:
“I testify that there is no true god (deity) but God (Allah), and that Muhammad is a Messenger (Prophet) of God.”
The first part of the testimony consists of the most important truth that God revealed to mankind: that there is nothing divine or worthy of being worshipped except for Almighty God. God states in the Holy Quran:
“We did not send the Messenger before you without revealing to him: ‘none has the right to be worshipped 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.
When someone pronounces the testimony with conviction, then he/she has become a Muslim. It can be done alone, but it is much better to be done with an adviser, so if you want to become a Muslim, do it without further delay.