A sales funnel is the step-by-step journey a potential customer takes — from first becoming aware of your product to actually making a purchase. It is called a "funnel" because many people enter at the top (awareness), but only a fraction make it to the bottom (buying).
Think of it like a department store. Hundreds of people walk past the window. Some step inside — that is interest. A few browse products — that is consideration. They talk to the salesperson, compare prices, and finally a handful of them pull out their wallet and buy — that is conversion. The entire process from walking past to checking out is the sales funnel.
Understanding your sales funnel helps you identify where you are losing customers and what to fix. If lots of people visit your website but nobody buys, the problem might be in your pricing, checkout flow, or trust signals — not your traffic.