All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Both of these books (“Al-Ibaanah” written by Abu Al-Hasan Al-Ash'ari and “Al-I'tiqaad” authored by Al-Bayhaqi ) which you mentioned in the question are important in determining the methodology of the Salaf (righteous predecessors ) in matters of belief. These are medium level books and it is more appropriate for a beginner to start with concise books like 'The Three Fundamental Principles of Islam', 'Clarification of Uncertainties' [by Mohammad Ibn ‘Abd Al-Wahhaab], and '200 FAQ on Islamic Belief', and other concise books for beginners.
The most important thing a seeker of knowledge should be concerned with is the Book of Allaah, memorizing it and reading its interpretation. Moreover, one should seek knowledge from a scholar who is known to be righteous and has a correct belief so that he would teach him properly and guide him in a proper way.
Allaah Knows best.