How do you write a poem (4 lines, 3 stanzas) about freedom of the human person?

You sit down and write it. That's how any kind of writing is done.

I might start by deciding what I think “freedom of the human person” means. Is it a physical state, for instance, or a mental or emotional state?

I might come up with an overarching metaphor for that freedom.

Then I might devise three different ways of considering or experiencing that freedom. One for each pov. Three stanzas.

Then I would simply create a poem from those ideas and that structure.