u enter your bank or card details into your user profile.
whenever u pay for something using paypal it will first of all use money that u have standing in your PayPal account, if there's not enough available it will automatically draw on your primary card or account.
Tell your mate, that while he is in his Paypal account to click on "Withdraw", this will then take him to a page where his account(bank) details are, ie, the card he opened the account with, unless he has been paid to an email address with no paypal account, he will have to register an account with a debit or credit card.
When he originally setup his Paypal account, he should have set up Bank funding. If he hasn't done so then he will now need to.
When he did/does his Bank Account will be credited by 2 small amouts around the 20p mark. When he gets his statement or checks online, he then confirms that amount with Paypal. After he does that Bank Funding will be setup nad he can transfer to and from, and even use Paypal to spend with and a Direct Debit will come off his bank account.