Enjoy this pmri video

float, lead lag buffer slack but not freefloat

http://www.youtube.com/watch?feature=player_detailpage&v=vHiPS9nlR8k

for understanding freefloat and total float, I suggest to go on this site

http://www.deepfriedbrainproject.com/2009/08/total-free-float-cpm-network-diagram.html

this thread is also good
http://terms.ameagle.com/2011/01/what-is-slack-what-is-float-is-there.html (remember here formula for FF given is for 0 start method. Given FF = ESs -EFp -Lag)

Recent example in other topic by  http://pmzilla.com/question-re-free-float-and-total-float  is based on start by1 method. there  FF = ESs -EFp -1 -Lag

Faisal , if you have any specific question I can reply that.