Applying a finish to a pen is just a matter of preference and utility of the pen.
I sand through stages to around 400, then I prefer a thin CA applied to a paper towel. Dab the paper towel to the pen. If I want the pen to really shine, I’ll apply several coats and a last touch with 1000 grit sandpaper followed by a thin coat of CA applied via paper towel.
As you can see, methods vary. Have someone show you their way and try it. Have someone else show you their way and try it.