You can find assembly instructions for the BrickPi3 here. We will need to assemble the case, attach the BrickPi3, the Raspberry Pi, the Raspberry Pi Camera, add an SD Card, and add batteries. To make the software easier to setup, Raspbian for Robots comes with most of the software you will need already setup. You will need at least an 8 GB SD Card, and you will want to expand the disk to fit the full size of the SD Card.
The centre pieces on each face, as you may have noticed from playing around with the cube, can't be moved to another spot, only rotated. So we can use this to our advantage by building around the centres. The best centre to build your first cross around is the white centre, as many guides and resources on the web start with a white face, so if you need to look up some steps and examples elsewhere, your cube will look similar to the one that is being used in other demonstrations.
If there are no more edges left on the top layer, then they are probably either inserted in the right place but flipped, or inserted in the wrong place. To get an edge out of somewhere it shouldn't be, just insert one of the yellow edges into that slot. This should get the edge out and on the top layer, ready for you to use the above instructions to insert correctly. Rubix Build