If you add the sub domain to use that directory as its web root directory, you don't need to do a redirect. A redirect is to literally redirect it. This is not needed for a sub domain, which already has its own web root. A redirect doesn't sound like what you want. Try just adding the sub domain first, and ensure it points to the proper web root directory and that you don't have any wild card for the primary domain that will override the sub domain's virtualhost, and ensure you have a wild card (or A or CNAME type) in the DNS zone file, too (if not its own zone file for the sub domain--though this is poor delegation and you should have it all in the primary zone only. Don't worry about this if you don't understand it, it'll still work if it's right, either way).
I go into Subdomains menu and create stuff.domain.com .then right below that on the same subdomain tab it shows setup redirection to map that subdomain to a folder..so i point it to www.domain.com/stuff.
i'm not actually going to the redirect tab..i do have 2 redirects but they are totally unrelated to the subdomain or this question... i just thought that once i went to stuff.domain.com the top browser address window would stay at stuff.domain.com and any file i navigated to inside the stuff directory would stay under the subdomain..is this not correct?
It should indeed retain the sub domain URL address of stuff.domain.com when you go to pages, files, sub pages/directories, etc. within that sub domain's web root, unless you have a redirect, absolute URL link pointing elsewhere or something such as that, yes.