Urgent question : Online payment by Paypal and other gateways

Hi everyone
When I started to make my own online store I thought the payment part would be easiest part. Well I was wrong.

I'v been googling alot but I can't find any way to safely accept creditcards on my website.

I'v already made the shopping cart which allows users select several products and when the user clicks on (Check out) button he/she gets redirected to Paypal website to pay for the purchase.

I do this by a simple HTML form.

BUT the real problem is that. what if the user doesn't pay for the product? what if he closes the browser after going to paypal? how do I know the payment is successfull?

I can describe myself as a good PHP programmer but I don't know anything about online payments.
Please help me find an answer to my questions.
It would realy help if you give me any ideas where to start

It's kind of urgent

Thanks / Behzad

re: Urgent question : Online payment by Paypal and other gateways

if you are using any payment gateway that wont stop a customer from clicking off the browser. there button is always there and pressable.

you need to read the paypal documents on how to program the api to your online store or web form....whichever one you use.....i know for a fact that if you want to know exactly if the payment was completed its a process that you have to read up on......i created a form to link to paypal and the royal mail for p&p pricings, that was hard work