Often, there will be a relationship between categories. For example:
Assigning each Employee to a Job Title
Assigning each Deal to a Sales Rep
In the first example, your primary category is Employee, and your linked category is Job Title.
To link categories:
click the + column in the far-right column (via the Data Tables) and select the Link to category option.
This will create an extra column in the data table, letting you assign each category item of the primary category to an item of the linked category.
There may also be multiple levels of linking, for example:
Each Employee has a Job Title
Each Job Title sits within a Department
Therefore every Employee sits within a Department via their Job Title
1 to 1 vs. 1 to many relationships
Linked categories have a 1 to 1 relationship, i.e. each category item in the primary category links to only one category item in the linked category. Each Employee may only have one Job Title, for instance.
Causal's categories are not designed for 1 to many relationships, i.e. one Job Title cannot sit within multiple Departments.