Question: how to use gmic in gimp?
Answer: Start the Gimp-G'MIC plug-in (Filters → G'MIC). At the top of the center pane of the dialog, make note of the number of available filters; it should be a few hundred. At the bottom of the center pane of the main dialog box check the “Internet” box; click on it until a tiny check mark appears (once suffices, usually).