I just put a pair on this weekend.
From under the car, loosen the two bolts on each side of the oil pan that hold the pans. Slip a pan on to these bolts and tighten them enough to hold the pan.
From the top, or if you have long enough arms, drop the bolt down through each of the three holes in the rail. Lock washer goes at the top of the bolt. The square nut goes below the rail (it looks odd, but I put a lock washer on the square bolt end also as this area sees a great deal of vibration).
The pans are not "precision fit" so you need to be able to run the rail end of the pan up the bolt from below.
Tighten the rail bolts, then the pan bolts (20 lbs. torque). You may find that the pan side may not be flush with the pan. As long as the pan bolts securely hold up their ends you are fine.
I noticed that the car seemed to run a little cooler with the pans changing the air flow through the radiator. We may also hope for a better engine to frame ground with the pans in place.
Hope this helps.