Start at the Turtle Rock Trailhead, just above the roundabout near the campground and Box Canyon. Drop down to the parking lot and look for the trail to continue to the left, at the end of the parking lot. Open (and close!) a gate about 20 yards past the parking lot. Continue on as you pass beaver ponds on your left.
There is a lot of braiding between the waterfall and the Beaver Ponds parking lot, but you'll be fine as long as you don't cross the creek. The trail ducks out to a parking lot and then back away to the left for the last bit as you climb back to the trailhead.
When in doubt, stay right. There are some tricky rock sections that up the difficulty of this trail, but most of it is fairly beginner-friendly. Mostly decomposed granite with some rock sections on the NE side. This is packed with hikers on summer weekends and evenings, but generally pretty clear on weekdays and shoulder seasons when it's too cold to camp or the campground isn't open.