How do I become a Muslim?
The Declaration of the Testimony (Shahada)
To convert [or more accurately revert] to Islām and become a Muslim, a person needs to pronounce the below testimony with conviction and understanding its meaning - with other Muslims present:
"Ash hadu Anla ilaha Illa Allah...Wa Ash hadu Anna Muhammad ar-Rasool Allah."
I testify that there is none that deserves to be worshipped except Allah [God], and I testify that Muhammad is the Messenger of Allah [God].
When someone pronounces the testimony with conviction, then he/she has become a Muslim.