Thank you for your email and it’s nice to see you embracing new technology! I’m Daniel, I work with Katherine to help answer questions for the Voicebrew community.
To answer your question, if the audiobook was purchased through Audible and you have your Amazon and Audible accounts linked, you can say “Alexa, read my audiobook” to begin listening.
You can find all the information about how to use Audible with Alexa here.
Hope that helps you begin listening to Caste!