Admin users can set up your departments and department categories by clicking on your avatar in the bottom left-hand corner of any WeTrack page and navigating to Settings > Users & Departments. The terminology of 'department' and 'department category' is customisable to however your organisation labels these functions - check out this article to learn how to make that change.
Departments sit within Department Categories, and it is that lower level, Departments, that can be applied to tasks, and that users can sit within. Department Categories are optional and can be used to group departments, which might be especially useful for reporting or filtering.
An overview of all tasks assigned to a department or department category can be found by clicking ‘Projects & Tasks’ in the left-hand sidebar and navigating to the fourth or fifth tabs, the ‘Department & Department Categories Homescreen’.