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Look at the values in the Master list on the bottom left of the screen. Highlight a value on the left side and check the box next to the appropriate entry on the right. You may choose as many as you need. Before moving to the next value in the Master list, click the Update button to save the changes. Repeat the process for each value in the Master list.
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After matching the values in both lists, click Save Master/Sub Changes. Click Close to exit field properties.
Now, when you add a New Record or edit an existing record, the choice you make in the Master list will only show the associated choices in the Sub list.