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
You will need to acquire a Merchant Account in order to process payments via Credit Card. These companies typically charge a percentage per sale. I cannot recommend you one at this time.
As for PayPal, there are free and paid services through them as well. You can use PayPal as your merchant account as well, I think I recall. (Correct me if I am wrong).
Regardless, a project like this will require a lot of reading, and testing by your part. Dealing with online transactions such as this, is an amazingly rewarding experience.