There are two ways from which you can receive money into your paypal account. This is how it works:
1) Someone sends money into your paypal account.
20 You request money from someone and then that someone sends the money into your paypal account.
Your paypal account and your credit card and your bank account are all different. Do not get confused into thtinking that they are one and the same.
When there is money in your paypal account. It just sits there. Same thing as there is money in your bank account. To get the paypal money into your bank account, you have to withdraw the money into your bank account(s). If you don't do this, the money in your paypal account just sits there.
You can also use the money in your paypal account to make payments to other people with paypal accounts.
As far as paypal is concerned, your credit card account is just their way of knowing that you exist. Think of your credit card as an international identity card. That's all it is in as far as paypal is concerned.
Hope this is clear.
RoRK