How To Translate Mesh Selection Using Geometry Script?

I’m trying to achieve a similar shape like the one below using geometry script in blueprint.
Where the middle portion is supposed to be translated up or down.

This is modeled using modeling tools:


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But using geometry script in blueprint I only get this far, it’s completely flat:

My Blueprint:

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Also I struggle with understanding functions like the one below? They Say they create a list, but there is no list is to be found…