What is the proper way to revert my local GIT repo to a specific date (commit)?

I want to modify the sources as they would have looked on a specific day.

I've read to run git reset --hard {HEAD} where {HEAD} is the commit to rest. Does that command truly reset the repo? That is does the command only reset indexes and leave the sources intact or are sources modified to that specific commit and all subsequent pulls are deleted?

I realize that resetting my local repo will mean a bandwidth hit when I restore everything. :)

Darrell