First, you want to greet them, so if you know their name you should address them (e.g., Ms., Mr., Sir, Madam. etc.). Next, you might want to asking how they're doing before getting into the bulk of your email. Then, you'd thank them for the books they sent, and maybe you could even mention a certain book you're excited to read. You could also mention that you'll tell them your opinion on a certain book after. Finally, include your salutations (e.g. Regards, Sincerely, Thanks, etc.).
[Your Address Here]
[Date Here]
Dear Sir/Madam,
I hope you are doing well. How are things in Trinidad?
This letter serves to express my gratitude and acknowledge that I have received the books that you sent me. Thank you so much for sending me those books. I am really looking forward to reading them. It was of great help to me.
Sincerely,
[Your Name Here]
*You can replace the "Dear Sir/Madam" with "Ms./Mr." or something else. Just make sure to use their proper pronoun when addressing them.
