From your attached bank account.

Or from a credit card, though that's going to probably be considered like a cash advance and have a fee attached. But your bank may charge a fee as well. So you should check out the fee issue either way.

The instructions are on Paypal. When you create an account you have to link a bank account or credit card to your Paypal account. When you elect to add funds, the linked account is debited that amount.