How do you create DFFs that are Related?

Summary:

Hello,

I am trying to have a user pick from a list (military services) and depending on what they pick, they will get a second list for Rank of person.

Does anyone have a basic outline of the steps to do to create this? I have created basic DFFs before. But never with parent/child relationship.

I am getting lost in the implementation guide.

Thank you!

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