Answer:
Its quite easy. Be sure the mattress is in the lowest setting. The safety rails came with the crib- hopefully you still have them-
Remove the front piece of the crib- by simply removing the screws. You will need these screws to attach the safety rails.
The metal bracket on the safety rail attaches to the metal mattress frame. Use two of the small screws that also came with the crib.
Look at some pics online if you are questioning which way the safety rails go, but really, its wicked easy and I did it in less than 15 minutes!!