You can use one of two available types for the Database Custom Fields: Autocomplete and Select List, depending on your preferences, with the option to select multiple values as well.
The Child Database Custom Field is a simple text box, whose value is filled automatically when the value for its parent changes.
The fields are used in the following JIRA operations:
- Edit an issue
- Create an issue
- Transitions on issue
The Child Database Custom Fields and Parent Database Custom Field should be on the same screen, context, in order to depend on each other.