How do I get my Android phone to speak text in the navigation voice? I know my phone is capable of text to speech because it speaks in Google Navigate.  Can I get this same voice to say other things?
There are several apps with TTS (Text-To-Speech) support, which enables them to "talk to you" -- so that's what you should look for on the Playstore: TTS. So a Playstore-Search for TTS will result in a bunch off apps ("At least 1000 results") matching your request.

Now you can close in by redefining "other things" to something more specific. Add that "more specific" term to your query by prefixing it with a "+" sign -- so e.g. a search on "tts +ebook" will give you ebook reader apps with TTS support (plus some self-reading books as it looks like), "tts +translation" some language translator apps (you say it in your language -- and they speak back in a foreign language; very useful when travelling in a foreign country, as long as they take the answer from the natives as well to translate it back).

Now you should have got the idea, and can continue with other examples :)