You are confusing a Poser Runtime called Downloads with your computer's Downloads folder. Not the same. I don't know MACs, but there HAS to be a folder on that computer where the zip files go to (on a Windows machine it is called Downloads). You need to go into that, extract the zip into it (to keep it simple) and then drag the contents of the Runtime folder from THAT into whichever Runtime you want to use from your Poser program--if you want to use the Poser Downloads runtime, that's fine.

Again, first find where your MAC's Downloads folder is located--that is where all those freebies download to. A simple Google search for 'where are my downloads on a MAC' may find the answer, I imagine.