adding new domain problems

I've added a new doming name to my hosting account. I tried adding it as an 'addon' but after following the steps in the tutorial to have the name servers pointed, it's the sub-domain that appears to be working and the link to the actual add-on domain doesn't work. Not sure where I went wrong. I deleted everything, and am about to start again, though I'd like some assistance so I don't make the same error twice. Thanks!