Explain How delivery date is calculated using backward and forward schedul

How can anyone please explain how delivery date is calculated using forward and backward scheduling

I want to have it broken down into the following steps

for eg for delivery date calculation following dates are used

Material Availabilty Date

Material Staging Date

Pick/pack time

Transportation PLanning date

Loading date

Goods issue date

Transit Date

Delivery Date

Can some one please give me an example and explain wht these dates are

for eg customer needs delivery date on 11/20/2008

how would the system cacluate whether it can meet the delivery date using backward scheduling

and if it doesnt meet how does the system do the forward scheduling

also i am not clear with the following dates

material avaialibilty date

material staging date

transportation date

can some one please explain me all this in detail

Thanks