How to trim facial hair into stubble beard?

You would use clippers with a guard for the main part. I would recommend wahl clippers with a #1 or # 2 guard. (The smaller the guard the shorter the cut) If that doesn't make it as short as you'd like it , you can remove the guard and raise the blade which would leave it slightly longer than what most would refer to as a 0. You would use a regular beard trimmer to shape the outline and the detail.