When you're completely finished with a note, click "Save and Sign" to finalize. Once a note is signed, diagnoses, plan items, and text are no longer editable, and additional diagnoses, plan items, or text cannot be added without first unsigning the note. However, signing does not affect your ability to add or edit charges. You can also append comments to signed notes.
If you have the Patient Portal enabled and have opted to have encounter summaries visible to patients on the Portal, signing a note finalizes it and makes the encounter summary available to the patient. The encounter summary shows everything in the note except (1) the text (i.e., your subjective and objective notes) and (2) the charges.