The conversion funnel is for configuring the rate at which visitors to your website, leads from marketing, etc convert into users/customers for this product. You can currently set from 1 to 3 stages in the funnel. A common funnel configuration is to have a first stage of Visitors, a second stage of Trials, and those convert into Sales. The percentage you enter is the percentage of leads at that stage who progress to the next enabled stage. So if you only have 1 stage called Visitor and set the percentage at 40%, that means 40% of Visitors will convert into sales. If you add a second stage called Trials and set it at 40%, that means 40% of Visitors become trials and 40% of those (for an overall percentage of 16%) become sales. You will be able to have leads from different sources (website marketing, Google Ads, direct sales, etc) enter the funnel at different stages.