The melody of Baby by Justin Bieber runs 544 notes across 89 bars, 3:06 long in Ab at 128 beats per minute. The tab sits almost entirely in the first two frets, one note at a time — no chords to barre and no strumming pattern to keep up with. A piano backing track plays the chords and bass underneath, so the line you are learning sounds like the record even at half speed.
Prefer to strum and sing it instead? Baby chords and lyrics.