installing wordpress on a subdomain

Okay this question is more so to do with sub-domains then it is with word-press. I don’t know where else I could get help with this so I thought I would at least try here.

I have my business domain that is “swl-pc.com” I am building an rebuilding a website for someone and will not transfer it over to the real domain till I have it completed. I would like to make a subdomain on my business server and install wordpress on it and build the site there and once it is build I will transfer it over to real domain as he needs to keep his current website live till I get the new one completed. I made a subdomain within cpanel and installed wordpress on it. It works fine if I manually navigate to the directory but If I try to use the sub-domain it does not work. Are there any steps I am missing when making a subdomain? All I did was go to my cpanel and create the subdomain and installed wordpress on it. Are there any other steps to create a subdomain that I am missing?