A funnel isn't the same as a website. Funnels guide customers through a controlled sequence designed to push them toward a specific action, like buying. Most websites let people wander off before they're ready.
I would say the difference between a funnel and a website is that you are directly leading your customers or your prospective customers on a journey to exactly what you want them to see. So instead of just showing them this page with a bunch of options, you're saying, I want you to see this specific thing, and then I want you to click on this, and then I want you to see this next specific thing, and then I want you to put in your credit card information, and then I want you to see this next thing, and you're really able to control that behavior and make sure that they are seeing what you want them to see in the sequence that you want them to see it in. That's how I would describe it. But you should probably read Russell's books because he describes it like the best.