Quick tutorial: Texturing a single face in blender 2.8+
Channel: Mike Heavers
Date: 2021-01-27

How to apply an image texture to one face of a 3d object in the latest versions of blender. As noted by Ivy Lelee - make sure you start in face select mode: at the top left switch from Object Mode: Edit Mode, and Select the icon that, when hovered over, says "Face Select".

Looking to rotate the texture? Here's a very quick video that shows you how to do that as well:

https://youtu.be/OgWVGseTusk