Set document category for later use as document class

I'm doing a basic tag ranking through the examples of the knime.

But I have a hard time understanding how the "Category to Class" node works because the file goes in without the classes and exits with the classes but I do not know how it does the process, it has no configuration and I can not reproduce the result of the example.

Has anyone been through this and could you help me?

(For example, I have a csv with 3 columns, the first is the id of the line, the second is a fairly large document and the third is the class of this document, my difficulty is to input this class in the model)