A little bit more on git reset and checkout

	HEAD	Index	Workdir	WD Safe?
Commit Level
reset --soft [commit]	REF	NO	NO	YES
reset [commit]	REF	YES	NO	YES
reset --hard [commit]	REF	YES	YES	NO
checkout [commit]	HEAD	YES	YES	YES
File Level
reset (commit) [file]	NO	YES	NO	YES
checkout (commit) [file]	NO	YES	YES	NO

*WD Safe means that this action will not affect files in the workdir

The order of underlying actions on HEAD, index and workdir is the following:
The reset command overwrites these three trees in a specific order,
stopping when you tell it to:
  Move the branch HEAD points to (stop here if --soft)
  Make the Index look like HEAD (stop here unless --hard)
  Make the Working Directory look like the Index

git reset file - is actually a shortcut for git reset --mixed HEAD file and does essentially unstage

Discrard all local commits on master:
git fetch --all
git log origin/master
to find the latest commit on the remote, and
git reset --hard c0mm1tID
to reset down to this commit

Source:

https://git-scm.com/book/en/v2/Git-Tools-Reset-Demystified#Summary

This presentation might also be helpful to quicly review some interesting git features:

http://ben-denham.github.io/git-advanced/#/