Position the newel post, using a carpenter's square. Align one leg of the carpenter's square with the edge of the stairwell and square the post to the other leg of the tool.
Equip your power drill with a flexible shaft to bore pilot holes close to the newel post.
Use the same flexible shaft to drive in screws to hold the post in place. Do not snug these screws, because you will remove the post later and then reinstall it with the railings attached.
