Delete all untracked files and folders in git

git-clean

git clean -f
If you want to also remove directories, run git clean -f -d.

If you just want to remove ignored files, run git clean -f -X.

If you want to remove ignored as well as non-ignored files, run git clean -f -x.

Note the case difference on the X for the two latter commands.

If clean.requireForce is set to "true" (the default) in your configuration, then unless you specify -f nothing will actually happen, with a recent enough version of git.