Late Start/Finish....Total Float - how calculated?

Hi,

I hope someone can help me here...I have a schedule which shows columns so Start, Finish, Late start, Late finish, Free float, and Total float.

For example, my activity start 14/2/08, finish 6/6/08, late start 8/5/08, late finish 14/5/08, free float 0.0d, total float -16d.

How are the late start/finish and free/total floats calculated.???

where does the -16d Total float come from??

If someone can help me I would be so happy, as I am working on a massive project and being beaten down by clients over this!!!

Thanks everyone!
Regards
Ben.