Hi there! My name is***** am a computer professional with over 15 years of experience with both Mac and Windows computers, phones, tablets, e-readers, and printers. It would be my pleasure to assist you with this. In order to effectively use your Kindle Fire for email, you have to allow the device certain permissions, so it can keep the email and contacts on your Kindle Fire synced with your Yahoo account. This is a commom practice. If you don't give Amazon(aka your Kindle Fire) permission to access your Yahoo account then it can't import your emails and contacts.
I understand that is sounds scary. They are just trying to be very upfront and aboveboard about how it all works. Does that make sense to you?