Answer by Schwern for Git safe restore to old commit and return to latest

I think you're asking how you do work based off an older version.

For example, you have commits like so...

* C [master] - added the cool thing|* B - fixed that annoying bug|* A - did that mundane task

You can see a view of your repository like this with git log --graph --decorate --all --oneline.

Now, for whatever reason, you want to do work off commit B. Make a branch from commit B. A branch is nothing more than a label on a commit. git-branch optionally takes a starting point for the new branch.

$ git branch B_branch B* C [master] - added the cool thing|* B [B_branch] - fixed that annoying bug|* A - did that mundane task

Now you have B_branch at commit B. Switch to that branch and make some commits. They will be on top of B. master will be unaffected.

$ git switch B_branch...work work work...$ git commit -m 'B commit 1'...work work work...$ git commit -m 'B commit 2'* E [B_branch] - B commit 2|* D - B commit 1||  * C [master] - added the cool thing| /* B - fixed that annoying bug|* A - did that mundane task

And when you're done, switch back to master. git switch master.