Setting up subdomain

Hello all.

I have decided to try out gitlab on my server. Unfortunately I am totally confused about the setup process!

I have installed gitlab using the instructions contained here:

After that the instructions state to browse to the hostname and login. But there is no mention of how the hostname is setup in the first instance? How do I set gitlab to run from a subdomain?

I found some instructions about setting an external URL here:

http://docs.gitlab.com/omnibus/settings/configuration.html#configuring-the-external-url-for-gitlab

So I did that and ran the reconfigure script as described.

After that, no files are copied to the subdomain I specified, and of course browsing the subdomain results in nothing at all.

So my question boils down to:

After downloading and setting up gitlab, how is it possible to serve it from a particular subdomain?

Thanks in advance for any advice