What must a new Muslim know about Islam that cannot be ignored, and what books do you recommend?

Praise be to Allah for guiding the brother to Islam. After he pronounces the two declarations of faith (Shahadatain), it is obligatory to explain their meaning to him and to gradually teach him the matters of religion, just as the Prophet, peace and blessings be upon him, commanded Mu'adh. So, he should first be taught the five daily prayers, then Zakat. The matters of purification and prayer should be explained to him simply. When their time comes, the matters of fasting and Hajj, and how they are performed, should be clarified. He should be taught from concise books on religion, such as "Al-Usul al-Thalathah" (The Three Fundamental Principles) and the sections on worship and morals from the book "Mukhtasar al-Fiqh al-Islami" (Concise Islamic Jurisprudence).