I think, in the current implementation, you can save draft content of an article (between "publish" and the cog icon) without immediately posting it. You can also pre-assign a series to it before publishing, in that case, a series that only contains one or less published post will not be publicly shown as series. But please let me know if things don't work this way.
Incidentally, you can't change the article order in a series now, so you'll have to post (or maybe create) articles in chronological order. It's one of wanted features in the base software.
I think, in the current implementation, you can save draft content of an article (between "publish" and the cog icon) without immediately posting it. You can also pre-assign a series to it before publishing, in that case, a series that only contains one or less published post will not be publicly shown as series. But please let me know if things don't work this way.
Incidentally, you can't change the article order in a series now, so you'll have to post (or maybe create) articles in chronological order. It's one of wanted features in the base software.