In order to add a bed note you need to go to Bed View, right-click the night where you want to add a bed-night note and click on Edit Bed-Night Note:

A pop-up window will appear. Here you can type the note and save it:

In order to delete a Bed-Night Note, double-click on it to open Edit window, remove the text and click on Save. If there is no text, the note will disappear from Bed View.

See also:

How to add a daily note