What is the difference between Text-to-Speech and TalkBack and Google Talk? (also, I am unable to open the TalkBack tutorial on my Samsung Galaxy SIII Neo Android 4.4.2 (it just crashes the Settings app)). Any idea where I may find a better tutorial? Thanks.
Talkback is essentially a screen reader, though somewhat more feature-rich since it can also access hardware like the vibrator. It's intended to be used system-wide for accessibility purposes. The Play Store listing describes it as "[...] an Accessibility Service that helps blind and vision-impaired users interact with their devices".
Google TTS is the voice synthesis engine that actually converts text to speech. If you have Talkback enabled and it wants to read a label aloud, it requests the TTS engine to take the text and generate an audible representation of it on its behalf before then playing the audio. Any app that needs voice synthesis can tap into this engine.
Google Talk is an instant messaging platform. It was succeeded by Hangouts and support was officially dropped in February 2015, though the app may still function. It is not related to Talkback in any way other than being developed by Google.