Write an article based on this summary:

Choose an appropriate urethane finish for the door. Use a bristle or foam brush to apply finish. Sand off any bristles that appear after the first finish coat. Reattach all hardware.
Stain colors the wood, but you also need to protect your hard work by applying an exterior urethane finish on the surface of the stain to seal and protect it. Finish comes in flat, semi-gloss or high gloss, and will need to be applied in several coats. Always follow the manufacturer's recommended directions.  Water-based finishes are somewhat more environmentally friendly, but can also result in that "peach fuzz" texture that the stain creates as well. Apply the finish using a similar application and buffing process, using the steel wool or sandpaper between coats. Wipe down the surface with a wet rag. Allow the wood to dry thoroughly before applying finish, sanding it lightly if necessary before you begin. Follow the same basic procedure and pattern for applying the finish, using long even strokes and a uniform coat with the brush. Use a cloth to wipe off and smooth out excess finish if necessary. Read the manufacturer's instructions to find out how long to wait between coats, usually somewhere between two and six hours. Apply at least two more coats for a thorough, even finish over the first coat. which will be more heavily sanded than usual for a finish coat. By the time you get to the last coat, you shouldn't be sanding at all. When you've applied all the coats of finish, let the door dry thoroughly and wipe it down with a clean cloth to make sure it's completely dust free and clean before hanging it back in place. If you removed the hardware from the door, reattach it as before ad get your door ready to hang back up in the frame. Have a partner help to hold it in place while you screw the fixtures back in and reinsert the hinge pin into place to complete the job.