The 8vb means to play an octave lower than written. The D that is written on the staff would be played as 4th string open D or 5th fret of your A string.
Because of the 8vb we will play it as our low open D.
This of course means we have to tune our low E down one whole step to D.

Please note: the metronome is playing at the same tempo for both half and full speed mp3's. This means the metronome would be ticking eighth's notes when you play along with the half speed mp3 as opposed to the more common quarter notes as with the Full Speed mp3.