Second, Slide the lower arm mounted near the bottom of the bag, and move it as far back as possible with out sliding it all the way off.
Third, secure the clips to the top rail of the rack by rotating the blue tabs towards the center of the rack (you should here a couple of clicks, and secures the bag to the rack preventing it from bouncing off of the rails)
Fourth, slide the arm towards the front of the bike so that it moves towards the tubes that run vertically, and finally rests between the rack tube and the wheel. (this is to prevent the bag from bouncing away from the bike)
****The mounting hardware is durable, and will last a long time with proper use and care. You will be able to break the plastic pieces if your force them, please be patient, the first time mounting a bag may take a couple of minutes.