Domain is likely banned in the subreddit or even in the whole site.
He means you can post your link on twitter and then post the tweet link on reddit, this is to avoid the above issue of domain bans.
There are several sites you can use to do this: any site where you can post links, but is popular/mainstream enough that reddit will not ban its domain.
Reddit is hard, but it's well worth it. Search "reddit spam" on reddit itself/google to see what the moderators are complaining about then copy the methods used by the spammers, this should get you started.
Like I said before, you will need a bot to do this efficiently.
