Hi irep,
As luck would have it, this particular problem of yours has already been solved neatly. You can find the solution, complete with example macro to download, here:
New folder according to current Finder-selected file, then move file inside?
As for where you went wrong with your current macro, I’ll let one of the far more knowledgeable and experienced posters handle why you’re getting “%tags%tags%” in the variable name (though I suspect that it’s because that’s the current contents of %Variable%nom%, though for what reasons I couldn’t say from here) but I can tell you that you’re effectively erasing the file name from the clipboard after copying it by setting the clipboard to your Nom variable after the copy operation, essentially undo-ing the copy before it can be of use. I suspect what you wanted to do was save the file name to a variable after it had been copied, and you most likely overlooked adding the “Set Clipboard to Variable” action, and ended up going straight to using the variable before setting it to the content (i.e. the copied file name) that you wanted.
At any rate, please do take a look at that other thread, as it really solves your problem in a much more elegant way and will hopefully give you an idea of what KM can do with native actions.