At the beginning it was necessary to install the Ubuntu Touch SDK to program applications. With the end of Canonical support, the SDK stopped receiving updates and is currently difficult to use. There are two options: use the virtual machine of the course that contains all the necessary tools or use clickable.
The first part of the chapter explains how to configure the Ubuntu Touch SDK. This part is already written and I see no reason to eliminate it at this time. In the second part Fulvio explains how to use the alternative recommended by UBports: Clickable.
In both cases the code of the applications is very similar and you should not have problems in using either tool. You can ask any questions in the resources associated with the course.