Using git, how do you reset the working tree to the state of the index?

Question

Situation:

1. Edit files
2. Add files to the index
3. Edit more files

Now we have three different states. The state of HEAD, the state

Answer 1

git checkout :/ discards all changes in the working tree and replaces it with what's in the index, regardless of the current working directory.

https://git-scm.com/docs/gitglossary#gitglossary-aiddefpathspecapathspec