Select pickup point - new plugin

[sandomatyas]

I want to write a shipping plugin which provides a dropdown list with a predefined pickup point list and the customer can select which is the best for him/her.
As I checked the code, I can create a new plugin and add the dropdown list to plgVmDisplayListFEShipment method which is okay but what is the correct way to get and store the user selected value?
Is there maybe a documentation/tutorial about this?