Asuming its a ripe one (brown not green) find the three 'eyes' at the blunt end of the nut. These are three soft parts which you can bore out. bore out two of these and empty the milk out. Holding the nut so that the pointy end is to the left (or right) i.e. the long axis is parallel with the ground. strike the nut sharply with a axe or hammer (dont use a knife you'll damage it!!). This works best if you hit one of the ridges that run around the nut. Have a cracking time... Hamish