Honestly, you don't need a book. There are plenty of articles on the internet. A few Google searches of "mortgage basics" or "mortgage 101" or something along those lines will point you in the right direction.
Your agent or loan officer should have went over these things in-depth with you. For any client I work with that has limited knowledge on the subject, I extensively explain the home-buying process (including financing) whether they want me to or not. I believe education is key to making informed decisions and I don't want any client to say "I never knew about that" when working with me. Better to over-educate than under-educate IMO.
Here's an article to help you get started: https://themortgagereports.com/19098/first-time-home-buyers-guide-the-basics-of-mortgage-sp16i. Hope this helps.
In case you are a visual learner -- you might want to check out YouTube as well.
Here's a good list to get you started there: https://www.youtube.com/results?search_query=mortgage+101
Here is a link to the Home Loan Toolkit booklet from the CFPB which goes over the basics. It also includes links to other resources. It's not super in depth but should give you a good overview of the process and key terms.
If you are looking for more in-depth book, like Mortgages 101 or something similar, I would recommend looking at the publication date and focusing on the most recently published books. A lot of the books published in the early 2000s are not going to be relevant because many of the loans offered back then are not available today. Guidelines and regulations change over time, so you don't want to be reading outdated information!
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