1. Go to Training › Exercises and click Create exercise.
  2. Fill in:
    • Image: a reference picture to recognize it in the catalog.
    • General: name, instructions and the URL or code of a demo video.
    • Details: movement, main muscle, equipment, level, specialty, mechanics, joint and your own tags.
  3. Save.

Tip: fill in the details properly. Once you have hundreds of exercises, they'll be much easier to find.