Searching in single notes is identical for searching process in Notepad or other applications.
Searching in all notes is performed with special dialog:
In search results list you can see all searched text occurrences (with line and column specified) in visible
and, in case the appropriate check box is checked, hidden notes. Double click on the list row will select
the searched text in appropriate note and make hidden note visible.
Also on this dialog you can clear search history.