This is a very basic but I have been unable to find the answer on the web.
Is it possible to
git rm, i.e. to remove a tracked file, from magit?
Magit does not provide a command that does
git rm (but if you opened a feature request, then I would probably add it eventually).
Meanwhile you can delete the file using some other method, e.g. using M-x delete-file RET <file> RET. Once you have done that refresh the Magit buffer using g and then stage the "deletion" of the file by moving to it in the list of unstaged changes and then pressing s.
Magit doesn't support
git rm. Instead, delete the folder in dired, and then stage the change.
You can also use ! to launch any git command.