simulating apt-get on gentoo

A package I wish to download has these instructions:

wget -O - http://content.runescape.com/a=946/downloads/ubuntu/runescape.gpg.key
| apt-key add -
mkdir -p /etc/apt/sources.list.d
echo "deb http://content.runescape.com/a=946/downloads/ubuntu trusty
non-free" > /etc/apt/sources.list.d/runescape.list
apt-get update
apt-get install -y runescape-launcher

I have downloaded the apt sources and have been reading it. However
its fairly large &
complex which will take me a while to figure out.
The gpg key was fairly easy, but I don't see how apt-get uses it yet.
I also don't see how apt gets the list of files to download, since
there is only a directory given.
I can't displayhttp://content.runescape.com/a=946/downloads/ubuntu in a browser.

Just wondering if anyone has anything helpful to shorten the process
of figuring it out.
I'm planning to create a cut down apt-get which just fetches the
files, but don't have much time most days.