To be a Muslim is to believe the following:
That their is only One God; Allah.
That Allah sent down Prophets to guide humanity and that Prophet Muhammad (peace be upon him) is the last and final Prophet of Allah.
That the Quran is the words of Allah, and it is the final scripture sent down to humanity.
To believe in the unseen such as the angels, the Day of Judgement, Heaven and Hell.
A Muslim is one who submits to the will of Allah and obeys His commands.
Muslim's must do the following:
Sincerely say the testimony of faith (That their is no God but Allah and that the Prophet Muhammad (peace be upon him) is His final messenger.)
Pray 5 times daily at appointed times (Salaah).
Give charity to the poor and needy (Zakat).
Fast from dawn to sunset every day in the Month of Ramadan.
Perform the pilgrimage in Makkah, if capable to do so (Hajj).