It is a plastic dome top feeder with an adjustment screw that enables you to raise and lower the top to allow only small birds into the 'tray' to feed. I suggest hanging it in a tree where you see the bluebirds etc perching as they are looking to hunt for those slow moving insects. Another good idea is to cut a couple of small branches of berries of some sort and twist tie them on the hanging arm to help attract the birds to the feeder naturally. Keep the top raised till the birds are comfortable at entering the tray. Do not place the feeder close to your regular feeder because the bluebirds are not usually attracted to a seed feeder.
Water is one of the most important draw for the bluebirds in the winter.
Be sure to use a heater to keep some open water for all birds. A tray feeder of some type could also be used but the Droll Yankee X1 has a life time guarantee. To use the wooden bluebird feeders means a lot of time for you to 'train' the birds to get comfortable to use it. If you have bluebirds around consider placing a nestbox for them to use as a roost. If you have nestboxes up already be sure to winterize them by stuffing weather stripping in all holes and vents.