You can set up and test a site before using the Addon Domain function in cPanel, but it’s important to understand what happens with an addon domain first.
Please read this article: How do I setup an addon domain?
The important part of the addon domain procedure is step three in the article above; you will define a directory name there.
Let’s go through an example.
The main domain on your account is “thebirds.com”, and you want to add the domain “finches.com”.
In order to set up and test the “finches.com” site before using the Addon Domain cPanel function, simply create a directory in the public_html folder (in this example, “finches”), upload the files for “finches.com” into the “finches” folder, and test it by going to: http://thebirds.com/finches
Once you are satisfied with the results, follow the procedure in our knowledgebase article above and be sure to use the same directory name you used for testing – in this example, “finches”.
Note that this does not allow you to set up email accounts in preparation. Unfortunately, cPanel does not allow this kind of functionality. You will have to set up the email accounts after going through the Addon Domain procedure.
When you are ready to create email accounts, you can find a video tutorial about that here: both are here: