To be a Muslim you need to believe that there is no god but Allah (S.W.T) and the Beloved Muhammed (S.A.W) is the Final Messenger of Allah (S.W.T).
Allah (S.W.T) is only one and no one is equal to Him.
He Alone is worthy of worship. He has no family.
He did not give birth to anyone nor was He born.
He knows and sees everything hidden or not.
He alone is the real owner of everything.
He is everlasting. He has no body and is independent.
He possesses every good quality and is everywhere.
Allah is the personal name of Allah (S.W.T) whilst Rahmaan, Raheem Aleem, Qadeer, Baseer, Ghafoor etc are names of his attributes (Descriptions of His qualities).
To believe in these attributes is part of Faith.
It is the Hadith of the Prophet (S.A.W) that :
During each day and night of Ramadan Allah (S.W.T) sets free great number of souls from hell, and for every Muslim, during each day and night at least one dua is certainly accepted.