Wa 'alaik salam. The best book to start with is the Noble Quran. In the back of it there's a concise explanation of Tawhid which is the foundation of the religion and of Shirk which is the most serious thing that Allah has warned us against. Once you have a decent understanding of this the next book that the scholars suggest is one called "The Three Fundamental Principles of Islam. Insha Allah this will be of some benefit to you.
Walikum Salam, Please give us a call and we can guide you based your current library and help you find books that will help you understand and practice the religion.
Thank you I called and spoke with rep he was great help
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