You can use this expression to transition between different activities when you're leading a group of people. For example, after a science teacher has finished explaining one topic he can say:
So now let's move on to Chapter 15, "Biodiversity".
If you're presenting a new piece of software at work, you can explain what it does first and then use this phrase when you want to start showing the audience how to use it:
So now I'm going to demonstrate precisely how that works. Take a look at the screen here...