How Does One Become a Muslim?

One becomes a Muslim by believing in the Two Testifications of Faith (refered to in Arabic as ash-Shahadatayn) and uttering them with the intention of leaving out blasphemy.

What are the Two Testifications of Faith?

The Two Testifications of Faith are:

In English

I bear witness that no one deserves to be worshiped except Allah and I bear witness that Muhammad is the Messenger of Allah

 In Arabic

أشهدُ أنْ لا إلهَ إلاَّ اللهُ
 وأشهدُ أنَّ محمّداً رسولُ الله
(ASHHADU ALLA ILAHA ILLALLAH, WA ASHHADU ANNA MuhammadAR-RASULULLAH)
 

Allah sent Messengers to educate people about their well being in this life and in the Hereafter, as well as to call them to worship Allah alone without associating partners with Him.