BINs help please reply

[armeros]

Now that I know what bins are, can someone explain how they work. From what I can gather different websites have different bin numbers, and you need a card with those bins if you want to card that website. That confuses me, so if someone had the wrong bin number, from anywhere in the USA ,they just cant shop at that website? can someone please clarify.
Lets say I wanted to card an egift card from a website, do I still need bins?
Do bins only matter for physical carding? what about virtual?