For how to do it you can see here
Download Cool Reader to run TTS on Kindle Fire
1) Hit the menu button
2) Choose “more”
3) Choose “read aloud”
4) Hit the forward control to start coolreader reading the text.
5) You can control volume and speed with the sliders.
Coolreader will not start reading by itself. You have to give it a kick, using the instructions above.
Video of text to speech on kindle fire
Since I wrote this post I factory reset my kindle. Today, when I read your comment I redownloaded coolreader from the link in this post (check the sourceforge site for more currrent software). I downloaded what is posted here. Coolreader works. Make sure you do this … when you have the book open in coolreader… then you can play text to speech kindle fire as well as any text to speech for kindle fire apps to read out your documents or ebooks
Text to Speech (TTS) on the Kindle Fire