The trail begins right off Kamehameha Highway almost directly across the road leading down to the boat ramp. From there you'll climb up a set of man-made dirt stairs and tree- branch railings.
Thereafter, the path becomes indistinct for several hundred yards and you'll have to blaze your own trail over several crumbly eroded areas. Eventually, you'll find yourself on a spur leading up to a distinct knob at the top of the ridge. That knob is your goal.
The trail becomes more distinct as you ascend higher. It also becomes slippery in some sections, rocky near the top, and narrow and crumbly right before the summit. Be careful and take it slow. Your prudence will be rewarded once you reach the top, for you'll have excellent views of Kahana Bay and Valley to one side and Punaluu Valley to the other.
When you descend, don't hesitate to do some butt-sliding on some of the steeper, crumbly sections. It's my belief that a dirty seat-of-the-pants is a better alternative to a bruised and cut body, which can happen if you happen to slip and fall while going down.
Good luck and enjoy Pu'u Piei. If you're careful, you'll have an enjoyable hike up a short but tough trail.