I am developing a website and I need to receive payments from PayPal and Credit Card, the thing is that I know nothing about this, and my question is where I can find some g
Create an account at paypal. Then you will have access to its webbased API's. It ships with decent documentation and support.
The same story applies to other decent credit card companies: just have an account and ask/look for its webbased API's. Your webapplication has just to call those API's.