You pretend to have a product, and try to sell it -- market it, advertise, etc. If you get people trying to buy it / use it, you know you're going in the right

You pretend to have a product, and try to sell it -- market it, advertise, etc. If you get people trying to buy it / use it, you know you're going in the right direction. So yes, basically you bullshit everyone with some mockups and a pretty website, to determine if anyone would even be interested in the thing you want to build.