Magic Shader changes your player model through its own shader files. It does not depend on OptiFine to make custom models work. Before you start editing, check that the pack is loaded and actually showing on your character.
Turn the pack on
1. From the title screen, open Options.
2. Find the menu that matches how your copy of Magic Shader was packaged:
- Shader pack: open Video Settings, then Shader Packs, which your shader loader adds. Select Magic Shader and click Apply or Done.
- Resource pack: open Resource Packs, move Magic Shader to the Selected column, then click Done.
3. If Magic Shader does not appear in the list, open the folder from that same screen. Check that the file sits directly inside the folder and is not buried in an extra subfolder.
Check that it's working
1. Load a world. A creative test world is easiest.
2. Press F5 to switch to third-person view. You cannot see your own model in first person.
3. Look at your character. Your model should now display the shape and look that Magic Shader provides, not the plain vanilla body.
4. Press F5 again to cycle through the front and back third-person views. This lets you inspect your model from every side.
If your character still looks completely vanilla, go back to the menu and confirm the pack is still selected. A pack that was dropped into the folder but never enabled will not do anything.