To use a module, you have to pick one from the left-side blade and drag it inside the gray area in the middle of the window. That's not all. Each module has an output, which is supposed to either be the final product or to be fed as some other module as input.
To be strict about it, the white blade on the left side comes with both modules and datasets; nonetheless, this chapter is calling everything modules.
Except for a few, the majority of modules also need an input. Once a module is selected, it will be highlighted and you can see whether it requests one or more inputs, along with which kinds of inputs are needed, and you can also see how many outputs it has, along with each kind.
Inputs are represented by little circles ...
