What is the correct order to install zen as an addon

[Cliff H]

Hi Guys, I am getting so confused.
I have a domain with an oscommerce site installed and up and running. Lets call it abc.com on shared hosting.
I want to build a site on the same server as an addon with zen cart called 123.com (I already own this name)
Can someone please tell me the correct order of installation to achieve this.

Do I install Zen 1st then create an addon?

I did this then went to addon domains in cpanel typed 123.com in the "New Domain Name:" box which then auto filled "Subdomain/Ftp Username: and "Document Root: " boxes.
Is this auto fill information correct by default?

Will I need new FTP details or just use the same as for abc.com?

After this I typed 123.com in my browser but got page not found.

I have now deleted all the files, new sql database etc and will be starting from scratch. Any help appreciated, many thanks, Cliff