Straight Forward Easy Instructions for Multi-Store Setup?

Hi,

So far the closest I've gotten to understanding how multi-store works are these instructions:
create 2 demo sub domains
subA.domain.com
subB.domain.com
and "point" both sub domains to the same folder on your web host.
i.e. public_html/shop
Install opencart to the first sub domain and then go through the admin and add an extra store.
So you'll have Shop1 subA.domain.com and Shop2 subB.domain.com both running the same code.

Q: How do I point a sub-domain to the /shop/ folder? I've tried an A record a CNAME record and neither of them work.

And something does not make sense: if OpenCart is installed to the /shop/ folder then why would I also install it to the first sub-domain?

Some easy-to-read-and-do instructions for setting up multi-store would be great!

Michael

Thank you! These are excellent.

Michael