Technical where the f... are my brakes

[repofrance]

whist comming down a gravel path my 2001 jtd multipla started to tell me my brake fluid was low. at the bottom i checked my levels and all was ok but as i set off the pedal was very soft and although the car pulled up ok the felt less effective. i now have a metalic rattle from under the car ( not sure where from ) and the hand brake does not work at all.
what has gone wrong

tim