Step 8: Assemble the cube.
Start with the core and bring the centers into contact with it. Make sure to get the right sides in the right place. The sum of any face and it's opposite face should be 7, and if the 1 face is on top, and the 2 face is towards you, the 3 face should be to the right and 4 to the left.
Next place the edges, and lastly the corners.
And that's it. Turn your cube and enjoy the fruits of your hard work.