You can now rush to Nodelet Settings and add the "Free Nodelet" to your list of nodelets. Once you've done that, how to use it should be obvious. But note that most changes to settings take one extra page load before you see the effect, so click the node ID number at the top of the page (for example) after you make a change if it appears that the change didn't "take".
If you try to stuff 60kB of data into your Free Nodelet (or any of the other text areas on User Settings and the related 'Settings' pages), you'll likely mess up your settings (and you are a freak).
Later I'll post instructions for how to add a link to your Free Nodelet such that clicking the link adds to your Free Nodelet a link to whatever node you are viewing (so you can use the Free Nodelet like the Personal Nodelet).
Note that PM-style CODE tags don't work in the Free Nodelet. I'm not yet sure if this is a bug or a feature.