How do I "move" my commits from "no branch" to an actual branch?
I made a mistake, and started making commits "to the last tag", which lands my commits in "no branch". They should have been applied at the head of an already existing branch. I have not pushed my changes yet. I've found a few other question for when commits are in the wrong branch, but now I have no branch, so I don't know how to handle this.
Preferably, I would like to erase my mistake entirely, and "move" my changes to the end of the right branch. If I must leave my mistake in the history, I need to merge them in atleast.
Answer
You are currently in a detached HEAD state. To resolve that, all you need to do is create a new branch with git branch <branchname> or git checkout -b <branchname>. That will leave you with a local branch you can play with, and even delete when you're done with it.
Branches in git are just pointers to commits, so if you create a new branch where you are the new branch will point to your current commit, and then you can merge it or whatnot.
Your "mistake" need not be erased, you simply created new commits on top of previous ones. You did not modify history or anything like that.
EDIT: In response to your comment, what you need to do is:
git branch temp
git checkout master # or any other branch
git merge temp
git branch -d temp