The Assassin 3D and Panther come with two cables attached to them.
The longer cable will plug into your computers game port. While looking at the back of your computer you should only see one connector that you could use to plug in this cable. If you see more than one connector Click Here to see the Game Port Diagnostics.
The shorter cable is for plugging in your joystick.
The connectors are a 15 pin D shaped connector, and can only be attached in one direction.
If you need a longer cable you will need to get one that is shielded. This is very important as without the shielding you will get interference that will degrade the performance.