to commonly asked questions.

Why is my computer talking to me?

Hey Scotty, have a voice telling me everything I am typing and doing,  what is this and how do I get rid of it and where did it come from.  
You've accidentally turned on voice over in Accessibility. It's a feature designed to assist people who may have sight impairments To undo this, go to system preferences/Accessibility then click on "Voice Over". Uncheck the box and you should be good to go once again.
This image is a theme.plist hack