Permissions allow you to add very specific permissions to WordPress users, roles and groups.
If you want to provide permissions for a whole post type, the best option is adding a Supplemental Role.
However, Permissions are ideal if you want to have much more specific permissions. For example, you can allow users to edit or view only Posts in a single category. Or you can allow users to edit only specific Posts and Pages.
- Go to Permissions > Groups.
- Edit one of the groups on this screen.
- Click the “Set Specific Permissions” tab.
First, you will be able to choose which post type you want to target:

Next, you can choose which permission to give: Read, Edit or Assign Term:

Next, you can drill down and decide exactly which Categories and Tags this permission will apply to:

It is also possible to add restrictions directly onto a Category or Tag. This tutorial shows how it can be done.
Here are some examples of permissions in action: