By saying “No one deserves to be worshipped except God, and Muhammad is the Messenger of God” while believing in it, is how a person becomes Muslim.
If a person was a non-Muslim, he needs to immediately become a Muslim by saying the declarations of faith, in Arabic this is referred to as “The Shahadah” or “The Two Shahadahs”. In Arabic this is: Ash-hadu Allaa Ilaaha ilallaah wa ash-hadu anna Muhammadar-Rasuulullaah. And it means “I testify there is no God except Allah and I testify Muhammad is the Messenger of Allah”. A person can testify in which ever language he/she wishes as long as they say what gives its meaning, and it is not a condition to say the words “I testify”. If a person chooses to utilise Arabic words, then he needs to pronounce them correctly for the embracing of Islam to be valid, so for example if he chooses to say Allah then he needs to say it validly, as oppose to Allah, or Alla; or for example if he chooses to say Muhammad, he needs to say it validly, as oppose to Muhammad or Mohammed. If a person is not accustomed to say Muhammad then he can use any other name for Prophet Muhammad, for example Ahmad and he can use Abul-Qaa-sim (which can be pronounced Abul-Gaasim).
It is valid to say, for example: “No one deserves to be worshipped except God, and Abul-Gaasim is the Messenger of God”.
Important Rule: To become Muslim one does not need to know details about Islam, he does not need to know how to pray, or how to fast etc. Rather it is enough to say the declarations of faith, while believing in them. After a person has done this, that is when he learns more about Islam.
Important Rule: If a person wishes to become Muslim, he/she needs to do so immediately. Do not delay by even a moment, a person does not need to wait until Friday, a person does not need to wait to see an Imam of a Mosque. Becoming Muslim is simple and easy.