A funnel is a currated and strategic path that guides potential leads through each stage of your buying journey. The main thing that differentiates it from your website is that each part of the funnel has only one action for your lead to take.
The only goal of your funnel landing page is to get the email address. The only goal of the thank you page is to encourage a second action. The only goal of the email sequence is to get the lead to the offer. The only job of the offer sales page or call is to sell the offer.
A funnel can begin on your website's home page but getting the visitors on that page to the next step of the funnel should be a priority on that home page.