I don't think you "place" an article as such, though you can send it to the editor for consideration. If you want to pay for a "sponsored editorial" (essentially an extended advert) you can do that, and it will usually have a note at the top saying Advertisement or similar.
You can email your article to the editor for consideration (contact email ads are all on the main HHO site). H&H retain the right to edit or indeed not include it.