Read volume up being pressed in android device

Hi all,
Im trying to read when volume up is pressed on android, I have no experience making plugins and indeed I think this might be the solution here (in the latest answes)

But I have no idea how to deal with java code in unity, I have read in the docs and it seems easy, looked to a few tutorials and its very specific to the component they are making so I dont know what I should add in my c# script to deal with this well. Anyway my question remains the same, if someone knows how to read the up volume when pressed thats what I search for. Thanks for any clue about this