Credit card set up?

Hello, (not sure if am in the right section for this) but:

I have been asked by a company to build them a website, where the customers can go online and buy stuff from them via credit card. I really don’t know how to do this, all I know is Flash and some very basic HTML. Is there ne thing else i need to know or is that enough??

Is there some kind of sercuity i need to set up on the website?? I have no idea, so if there’s any links that some one could give me to help then that would be great.

thanks!!