Also called the sales process, a sales funnel is close to UX {user experience}. It refers to the experience you engineer for your audience as well as the line up of products and offers that you will make to them over the course of your relationship.
Creating a sales funnel is a VITAL component to have done BEFORE driving traffic to your blog, landing page, sales page, etc. Failure to do so will result in lost time, money, and visitors.
Here's a crude example of a sales funnel:
Traffic{solo ad}--->squeeze page--->one time offer {$7}--->confirmation/welcome email--->free prize--->email series--->affiliate offer--->email series--->affiliate offer--->email series--->content--->email series--->high ticket item.
See how that works? You engineer the user experience and decide on the content and offers you will show your audience {buyer persona/customer avatar} before you ever go to work on your project...and certainly before you drive traffic.
Hope this helped explain it all for you.