bar placed on your back , like squats... and you bend over like u would be touching your toes... but keep hands on the bar, hjaha this works the lower back
If you want to do them properly, concentrate more on shoving your ass backwards rather than bending over forwards. Will really hit your hamstrings and lower back.
Yes, like Backlash said, make sure your center of gravity remains on your hips. Just behind forward will put severe strain on your lower back (lumbar spine, I guess?).