Customer Account

Im a little lost in how to create a customer credit account where I can give out a receipt with the total amount, balance owed and the payment amount.
For example if somebody orders something but pay only 50% of the total sell I would like to have that printed out with the balance as well. Ive been Using the Simple Reservation and I like how it allows me to close the working period.
How can I combine these two features .
Thank you