Here are the steps to install a stair railing:

1. Measure the stair and purchase the stair railing.
2. Locate the studs in the wall above the stairs.
3. Plumb up from the front edge of the top stair nosing to mark the height of the handrail.
4. Cut the rail to length and fit the joint.
5. Close-Up: Cut a 45-degree miter on one end of the rail.
6. Test the fit.
7. Glue the joint with epoxy.
8. Install mounting brackets on each stud.

For more detailed instructions, you can check out this article from **The Family Handyman** or this video from **This Old House**. I hope this helps!