The more I read, the more it seems the less that I know

I bought a kindle HDX fire and calibre companion&moon+reader pro from the amazon store. My question is do I need to download them first to my android tablet and then sideload them to my fire? It seems from what I have read on this forum that I should follow that procedure....I hope somebody can further advise me with this. I really like this tablet but need moon+reader for my epubs.