Discard staged content.

Unstage content from a specific file or folder

git reset path/to/folder

Now typing git status you’ll see them unstaged. Need one more step back, to discard them at all

 git checkout path/to/folder

You are done.

Please done that executing git checkout against a branch will checkout (switch) to that branch.

Now if you have this time files [new files] that are not part of the repository, get rid of them

git clean -fd

You can simulate it if unsure.

Now, you want to revert a wrong commit

$ git log -2
$ git revert 909989890

Where 909989890 is the commit to be reverted (undo).

This command will create a storno commit (another one that will fix the previous).