Step 4: The lower part
Body - Begin with the Screen, as you can see it is lifted on the level of the buttons. Attach the pieces with the buttons and the pads to the sides and the shoulder parts (page 1) to these pieces. That one with the white status-light is belongs to the right. You can find a reference picture for the circle pad beneath, the first ring goes to the inside of the hole and the grey part comes out.
When you now add the bottom piece, make sure that you leave the hinge-end open.
Buttons - I think those are self-explaining (Button-order: X, Y, A, B)