The Personal Nodelet provides a place to store small snippets of HTML (including PerlMonks-specific markup). (Currently, each snippet is limited to a length of 1024 characters.) Each time you fetch a page from PerlMonks, these snippets of html are rendered in your Personal Nodelet (assuming you've enabled it in your Nodelet Settings). A line break (<br>) is inserted between each one.
General management of the your Personal Nodelet contents is provided by your Personal Nodelet Settings. On that page, the raw html of each item is shown (and editable) in the text fields on the right, and the way PerlMonks will render each one is shown in the middle.
Although it is of more general usefulness now, the original idea of this nodelet was as a mini bookmark list and "link collector"; and its current design shows that heritage. Notice these several links at the bottom of the nodelet:
The other two links add a link to the node currently being viewed to your public or private scratchpad, in case you like the idea of using those places as bookmark collectors.