Price Comparison with PHP?

[vcm]

Hi All,
I'm new to the forum. I'm wondering if anyone can tell me in simple terms, how price comparison sites work? How do you make a price comparison site? Is it done with PHP and SQL?

Also, how do Insurance sites work, and search through lots of compaines to find all the quotes?????

I would be most greatful if someone could break this down for me.

Many thanks, Craig