The Resource Categories are used only to group the resources in the Resource Situation View.

You may want to group the resources in categories in order to spot resource bottlenecks, which may otherwise be hidden when the supply and demand for resources are calculated across all resources.

Below this situation is depicted:

The resource situation across all resources.

The resource situation for bricklayers. No demand for carpenters hides the surplus demand for bricklayers.

The resource categories are not semantically linked to competences. But the demand for resources are using the competences of the required resources pr. activity to look up the resource category of the resources possessing those competences. See Resource Situation View for details.

See here how to create resource categories.

See here how to assign a resource category to a resource.