Notice the pattern of little plastic pegs attached to the palmrest tray. These pegs fit into the bottom of the keyboard to help keep it in place.

Also notice that the tabs on the top of the keyboard will fit inside the tab openings toward the top of the palmrest

Don't forget about the keyboard data cable that is underneath the keyboard. You will need to feed the data cable down through the palmrest opening and then connect it to the MB on the opposite side.