The training categories are displayed in the Training catalogue and make possible to filter the list of trainings according to a precise category.
As a content manager (or administrator), you can manage these categories. To do that, just open the admin menu by clicking on the related pictogram on the top right toolbar, then on "Manage categories":
You will then arrive on that interface:
You can click on "Add term" button in order to add a new category.
To manage the existing ones, just click on the pictogram under "Operations" column, what will offer links to edit them or delete them.