By default git revert refuses to revert a merge commit as what that actually means is ambiguous. I presume that your HEAD is in fact a merge commit.

If you want to revert the merge commit, you have to specify which parent of the merge you want to consider to be the main trunk, i.e. what you want to revert to.

Often this will be parent number one, for example if you were on master and did git merge unwanted and then decided to revert the merge of unwanted. The first parent would be your pre-merge master branch and the second parent would be the tip of unwanted.

In this case you could do:

git revert -m 1 HEAD

git cat-file -p [MERGE_COMMIT_ID] will show the parent branches in order. The first one listed would be -m 1, the second -m 2.

This depends a lot on what you mean by "revert".

Temporarily switch to a different commit

If you want to temporarily go back to it, fool around, then come back to where you are, all you have to do is check out the desired commit:

# This will detach your HEAD, that is, leave you with no branch checked out:
git checkout 0d1d7fc32

Or if you want to make commits while you're there, go ahead and make a new branch while you're at it:

git checkout -b old-state 0d1d7fc32

To go back to where you were, just check out the branch you were on again. (If you've made changes, as always when switching branches, you'll have to deal with them as appropriate. You could reset to throw them away; you could stash, checkout, stash pop to take them with you; you could commit them to a branch there if you want a branch there.)

Hard delete unpublished commits

If, on the other hand, you want to really get rid of everything you've done since then, there are two possibilities. One, if you haven't published any of these commits, simply reset:

# This will destroy any local modifications.
# Don't do it if you have uncommitted work you want to keep.
git reset --hard 0d1d7fc32

# Alternatively, if there's work to keep:
git stash
git reset --hard 0d1d7fc32
git stash pop
# This saves the modifications, then reapplies that patch after resetting.
# You could get merge conflicts, if you've modified things which were
# changed since the commit you reset to.

If you mess up, you've already thrown away your local changes, but you can at least get back to where you were before by resetting again.

Undo published commits with new commits

On the other hand, if you've published the work, you probably don't want to reset the branch, since that's effectively rewriting history. In that case, you could indeed revert the commits. In many enterprise organisations, the concept of "protected" branches will even prevent history from being rewritten on some major branches. In this case, reverting is your only option.

With Git, revert has a very specific meaning: create a commit with the reverse patch to cancel it out. This way you don't rewrite any history.

First figure out what commits to revert. Depending on the technique chosen below, you want to either revert only the merge commits, or only the non-merge commits.

# This lists all merge commits between 0d1d7fc and HEAD:
git log --merges --pretty=format:"%h" 0d1d7fc..HEAD | tr '\n' ' '

# This lists all non merge commits between 0d1d7fc and HEAD:
git log --no-merges --pretty=format:"%h" 0d1d7fc..HEAD | tr '\n' ' '

Note: if you revert multiple commits, the order matters. Start with the most recent commit.

# This will create three separate revert commits, use non merge commits only:
git revert a867b4af 25eee4ca 0766c053

# It also takes ranges. This will revert the last two commits:
git revert HEAD~2..HEAD

# Similarly, you can revert a range of commits using commit hashes (non inclusive of first hash):
git revert 0d1d7fc..a867b4a

# Reverting a merge commit. You can also use a range of merge commits here.
git revert -m 1 <merge_commit_sha>

# To get just one, you could use `rebase -i` to squash them afterwards
# Or, you could do it manually (be sure to do this at top level of the repo)
# get your index and work tree into the desired state, without changing HEAD:
git checkout 0d1d7fc32 .

# Then commit. Be sure and write a good message describing what you just did
git commit

The git-revert manpage actually covers a lot of this in its description. Another useful link is this git-scm.com section discussing git-revert.

If you decide you didn't want to revert after all, you can revert the revert (as described here) or reset back to before the revert (see the previous section).

You may also find this answer helpful in this case:
How can I move HEAD back to a previous location? (Detached head) & Undo commits

My favorite way (the cleanest possible) to revert a commit is to use git reset

Basically, these are the steps I follow:

1. Get the commit code to revert to (either with git log or going to the repository's history)
2. git reset <code> --hard to return to that commit
3. Backup the entire project somewhere else in the computer
4. git pull to return to the latest commit
5. Erase everything and paste the previous backup
6. git add . (at this point, all the changes that have been made since the commit you've hard-resetted to, need to be staged)
7. git commit
8. git push

I know it may take some time meanwhile some codes do this automatically, but I think it's the safest way if you don't have permission to force-push.

If you can force-push (and this is very dangerous, since you actually erase all history from the repo after the commit you are returning to), you simply have to hard reset (just like point 2 above) and run the command git push --force

git revert makes a new commit

git revert simply creates a new commit that is the opposite of an existing commit.

It leaves the files in the same state as if the commit that has been reverted never existed. For example, consider the following simple example:

$ cd /tmp/example
$ git init
Initialized empty Git repository in /tmp/example/.git/
$ echo "Initial text" > README.md
$ git add README.md
$ git commit -m "initial commit"
[master (root-commit) 3f7522e] initial commit
 1 file changed, 1 insertion(+)
 create mode 100644 README.md
$ echo "bad update" > README.md 
$ git commit -am "bad update"
[master a1b9870] bad update
 1 file changed, 1 insertion(+), 1 deletion(-)

In this example the commit history has two commits and the last one is a mistake. Using git revert:

$ git revert HEAD
[master 1db4eeb] Revert "bad update"
 1 file changed, 1 insertion(+), 1 deletion(-)

There will be 3 commits in the log:

$ git log --oneline
1db4eeb Revert "bad update"
a1b9870 bad update
3f7522e initial commit

So there is a consistent history of what has happened, yet the files are as if the bad update never occurred:

$ cat README.md 
Initial text

It doesn't matter where in the history the commit to be reverted is (in the above example, the last commit is reverted - any commit can be reverted).

Closing questions

do you have to do something else after?

A git revert is just another commit, so e.g. push to the remote so that other users can pull/fetch/merge the changes and you're done.

Do you have to commit the changes revert made or does revert directly commit to the repo?

git revert is a commit - there are no extra steps assuming reverting a single commit is what you wanted to do.

Obviously, you'll need to push again and probably announce your balls-up to the team.

Indeed - if the remote is in an unstable state - communicating to the rest of the team that they need to pull to get the fix (the reverting commit) would be the right thing to do :).