These are super easy, the main thing to take care of ahead of time is that the surface of the handle is clean, and relatively cool. If you have a little stool you can sit on, grab that, and position yourself at eye level to the door handles.
Carefully remove the decal/trim from the white backing sheet, ensuring the vinyl stays attached to the clear carrier sheet.
Now present the decal to the handle (holding it by the clear transfer film) and, looking at all the edges and corners, gently apply it with a very light touch, in case you need to re-position it. Once you're happy with the position, apply firmer pressure (maybe using a microfiber cloth, or something else that will evenly spread the pressure). Finally, remove the transfer tape by gently and slowly pulling back at a sharp angle.
Here's a video to show the process: