if i'm understanding you correctly, you have a bank account, but don't know the appropriate routing numbers, etc. to set up the paypal account. i'd suggest you go to your bank and see if they can help provide you the numbers you need or talk to your parents and see if they can help you set it up with their account.
otherwise, one other way you could possibly pay is transferring money through a bank account service... like if for example, you both have bank of america, you can transfer money from your account to someone elses account. i'm not sure how secure that is in purchasing situations though.