Please help with my spreadsheet

Hello,
I am having a hard time trying to figure out how to format my spreadsheet so that i can make it a template that i can use in future, this is what i have to work with, a course being offered at the local tafe is due to start on 12/12/2012 (hypothetically), if the students pay within 7 days of the course starting that get no discount, 7-13 days they get a 5% discount, 14 - 20 days the get a 8% discount and 21 days or more they get a 10% discount.
i need to create and enter formulas that will calculate the number of days paid in advance, the discount they are entitled to and the course fee paid. i hope some one understands what i have just written like i said i am desperate i feel like my brain is going to explode, i am studying business studies and i have answered every other question but i just cant for the life of me figure this out and its a stand alone task meaning there is no text available for this, i should add i have recently given birth and i missed a few weeks of class so im guessing this is one of the things i missed. thankyou for your time you will never know how very greatfull i am.