Take out the upper case (the one with fan holes) from the package.
Align the fan with the four posts, note the sicker side of the fan should be facing up.
Secure the fan using two screws with washers.
Take out the lower case from the package. Place the Raspberry Pi board into the lower case. Note there are posts on the lower case used to align the board. Make sure the Ethernet and HDMI openings align correctly to the corresponding ports on the Raspberry Pi board.
Connect the wires of the fan to the Raspberry Pi GPIO. Note the positions of the red/black wires. The red wire should be on the first row, second pin from left.
Fit the upper and lower case together.
Use 4 small screws to secure the upper and lower case together.
Take out the four rubber pads from the package. Stick them to the two indented circle on the bottom of the Raspberry Pi case.
The assembling of ABS case is finished.