When you drive on the roads, you know where you are on those roads. Each road has a name or number. Each town has a name. And each house has a number. If you are at house #100, you can go back to #50 or forward to #150. You can look at the signposts for directions. And you can look at your atlas for the structure of the roads in detail. In other words, it is easy to navigate the roads. You cannot get lost. But when you give a presentation, how can your audience know where they are? How can they know the structure of your presentation? How can they know what is coming next? They know because you tell them. Because you put up signposts for them, at the beginning and all along the route. This technique is called 'signposting' (or 'signalling').