trying to create a subdomain, need to find out how i can use cs cart with that subdomain and also my main domain
Where are you locating your sub-domain? This is primarily a cpanel change where your alternate store is in a diffrent location (or a sub-directory of your existing store).
If you do it in a sub-directory, make sure you fix robots.txt so that search engines starting in the parent store (primary domain) do not crawl the sub-domain.