You'll need a pastry bag, scissors, a plastic coupler and ring, and pastry tips. Twelve-inch disposable pastry bags are the right size for beginners (and professionals) to use, especially for a gingerbread house, where a larger bag would get in the way. Any kind of pastry tips will work, but for straight lines, a #10 plain round tip is good for bolder lines and a #2 plain round tip is best for finer lines.
It's a good idea to use a pastry coupler if you intend to change pastry tips, like from a star-shaped tip to a writing tip, and so on, on your project. Otherwise, if you just slip the metal pastry tip into the bag without a coupler, you'd have to completely empty the bag to change tips. Or you would have to start another pastry bag and have three or four with different tips going at the same time. Too much bother, if you ask me!