Assalaamu alaykum .I have read some books on Aqeedah (creed), like Kitaab At-Tawheed by Muhammad ibn Abdul Wahhaab, ‘Aqeedah At-Tawheed by Saalih Al-Fawzaan, and Fiqh As-Sunnah by Ahmad ibn Hanbal. I did not see too much of a diference between them. Later, I heard about classical books like ‘Aqeedah Al-Waasitiyyah and ‘Aqeedah At-Tahaawiyyah. My question is: what are differences among them? Is it a must to read all of them? What is the basic requirement? Please explain.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

All these books are good; they establish the ‘Aqeedah of the Salaf (righteous predecessors) in general, but they vary in the topics which they deal with. Some of them may deal with some topics, while others do not. If you want to benefit from them, you should start with the small ones before the big ones; that is the best method.

Al-Bukhaari said in his Saheeh: “Ibn ‘Abbaas, may Allah be pleased with him, said: {Be pious scholars of the Lord.} [Quran 3:79]; i.e. forbearing and versed in Islamic knowledge; and it is said: a pious scholar of the Lord is the one who educates the people with the small matters of knowledge before the big matters.”

The best of all this is to learn at the hands of a shaykh who explains what is difficult and clarifies what is ambiguous, in addition to other matters that the student of knowledge needs. This is in addition to the morals and manners that the student of knowledge learns from the shaykh, because knowledge without morals and manners may be a disaster for the person who possesses it.

Al-Aadaab Ash-Shar‘iyyah authored by Ibn Muflih reads, “Ibn Al-Mubaarak said, ‘Makhlad ibn Al-Husayn said to me, 'We are more in need of more manners than we are in need of much ahaadeeth.'’”

Finally, we do not know what you meant by "Fiqh As-Sunnah" by Ahmad ibn Hanbal; perhaps you meant "As-Sunnah" by Abdullah, son of Imaam Ahmad ibn Hanbal.

Allah knows best.