You will need the following tools : 1 x Posidrive screw driver
Firstly place the two supplied 11mm standoffs in the Raspberry Pi board. Put them in the 2 holes opposite to the header, screw them in tightly.
Next place the supplied 2x20 header onto the Raspberry Pi :
Now place the Pi In The Sky board on top of the header, it should click securely in place :
Finally screw the remaining two screws in to the stand offs to secure the board in place :