Well, you may have turned on Speakable Items, or Voiceover, but I'm not a Mac person..
If it's Voiceover, hit [Command (apple key)], [Fn] and [F5] to turn it off, or you could do this system prefs > universal access > turn voice over off..
I am pretty sure it's Voiceover, as it puts black boxes on icons, windows, and whatever..
(I did a Google search...)
Although, if the "talking man" doesn't stop, there always is a mute option...