The eight pins that you are talking about must be divided into four pins on either sides of the switch. Let me tell you something about one of the sides and the similar applies to another side as well. Out of these four pins just short two pins in the middle together, this point serves as the common pin. Rest is the same, connect the uppper pin of one side with the bottom pin of another side and repeat it for the other side as well, forming an X shaped connection.
Now connect your power supply terminals(GND ,VCC) with the two common pins at middle, on either sides i.e. VCC on one side and GND on another. After this connect one terminal of motor with any one of the remaining pins (out of 4), at corners. Also connect the motor's second terminal with the pin just oppsoite (on other side) to the pin that you chose.
This finishes with your task of making a DPDT switch which could control a DC motor in both the directions, clockwise and counter-clockwise.
Hope this helps