1. Create a new incident type or edit an existing one.
2. Mark a field as "Conditional and then select the type as "Role"
3. Select the role or roles that should be able to see this field.
Things to note:
1) Conditional's can apply to Role or previous field conditions. They cannot apply to Roles and previous field conditions at the same time for the same conditional.
2) Role permissions also apply to public forms.
3) You cannot hide by role for an entire section, this needs to be defined at the field level.