The next trail is headed "Interfaces and Inheritance". I have already suggested that real beginners can manage without this stuff, and I think they could safely skip this trail.
I shall plough on, because my last project used a lot of code, and if I am starting again in a new language, I might as well familiarise myself with any techniques which might make my coding more efficient.
Reading the blurb on Interfaces it seems these might be used in large collaborative projects, where different, possible competing entities write code, but they agree to operate within a common structure; and that's where the interface comes in. The vendors of programming software might also use them.
Inheritance has already been explained quite well with the bicycle analogy, and these lessons just seem to flesh that out a bit further. Placing an object at the top of the superclass hierarchy seems typically contrary, but at the end of the day, if it works, who gives a shit.
In summary, this trail is a reference trail. If anyone ever needed to use these constructs they'd refer to it.