We're currently overhauling the Rockpool UX/UI to make it better/faster/shinier and will put together the coding part when that's done ( otherwise the video will be out of date immediately ).
It's actually remarkably simple to get a basic line-following robot. We've done it with red tape on a white background and just 4 simple rules:
Light Visible -> Speed
Light Visible -> Invert -> Speed
On -> Rainbow Green
On -> Rainbow Blue
You will have to experiment a little to pair the right light sensor with the right wheel, in my setup I've got light on channel 4 paired with the motor on channel 3, and Light on channel 5 paired with the motor on channel 6.
You can then use Add/Subtract to tweak the light input value to match the ambient light in your environment.
There are dozens of other ways to solve the problem too, but when it works this one is by-far the simplest.