Reset

To demonstrate the various reset commands we need a repo containig 3 versions of a file:

$ git init

$ echo V1 > file.txt
$ git add file.txt 
$ git commit -m"V1"
[master (root-commit) 1532be9] V1

$ echo V2 > file.txt
$ git add file.txt 
$ git commit -m"V2"
[master bd670b5] V2

$ echo V3 > file.txt
$ git add file.txt 
$ git commit -m"V3"
[master 5a4e185] V3

After these commands the repo contains 3 commits:

$ git log --oneline --decorate 
5a4e185 (HEAD, master) V3
bd670b5 V2
1532be9 V1

reset acts upon the commits, the INDEX and the working tree. At this point all three are in-sync:

HEAD         V3
INDEX        V3
Working tree V3