You need to link a bank account with paypal, log in, then go to profile, click on bank account, then set up a bank account and set it as primary to receive funds, then you can use the 'withdraw' feature, you will be charged 25 pence if the amount is up to £49.99, over £50.00, it is free to withdraw the money.
Also when you receive a payment by paypal you may end up paying a fee to receive the money because the payer has a credit card listed as their primary payment option in paypal, most people leave their credit card listed as the primary payment method and not a linked bank account that does not charge a fee.
To use any money stored in paypal to pay your ebay fees you need to log into ebay, click on my ebay, look in left hand column, select seller account in the my account section, then you have the optio to pay by paypal or a one time payment.