All praise be to Allah, the Lord of the universe. May peace and blessings of Allah be upon Mohammad, His last messenger.
"Some people have a wrong notion that entering into the Islamic fold requires an announcement from the concerned person in the presence of high ranking scholars or shaikhs or reporting this act to courts of justice or other authorities. It is also thought that the act of accepting Islam, should, as a condition, have a certificate issued by the authorities, as evidence to that effect.
We wish to clarify that the whole matter is very easy and that none of these conditions or obligations are required. For Allah, Almighty, is above all comprehension and knows well the secrets of all hearts. Nevertheless, those who are going to adopt Islam as their religion are advised to register themselves as Muslims with the concerned governmental agency, as this procedure may facilitate for them many matters including the possibility of performing Hadj (Pilgrimage) and Umrah."
To become Muslim, you have to pronounce the Testimony of Faith 'Shahada', with sincere faith.
The implication of the Shihada is that you believe that there is only one God, Allah, Who alone deserves to be worshipped. It also implies that you believe in Muhammad, peace be upon him, as the Messenger of God, and you believe in his message. It also means that you believe in all of God's Prophets, including Jesus, peace be upon him, who is a Messenger of God and NOT divine or son of God.
If you accept this, the only thing that remains for you to become Muslim, is to say the Shahada, while believing in it with your heart word for word as follows:
"I bear witness that there is no God except Allah, and I bear witness that Muhammad is the Messenger of Allah"
then repeat this same testimony in Arabic as follows:
"Ash hadu anlla ilaha illallah, wa ash hadu anna Muhammadan rasul ullah"
Of course faith is not only words but is complemented with action, so upon reciting the Shahada one should begin to learn and uphold his/her duties as a Muslim. The main pillars of Islam as you know are:
The Five Daily Prayers
Annual charity to the poor and needy
Fasting the month of Ramadan
Pilgrimage to Mecca (once in a life time for those who are able)
The next step now after the Shahada is to take a complete shower (bath) with the intention of purifying yourself to be ready for prayers.