Perform actions on notes
In Sierra, you could swipe two fingers across a note in the list to reveal a delete button (and continue swiping to delete the note). In High Sierra, the leftwards swipe still brings up the red delete button, yet it’s joined by a grey lock button. Locking a note stops it being edited. This used to require choosing a menu command.
New in High Sierra is the ability to pin a note to the top of the list. With the pointer over a note there, swipe two fingers right a little way on your trackpad, or one on Magic Mouse, then keep swiping or click the Pin button. Or, choose File > Pin Note, or Ctrl-click a note. If you do this a lot, set a key combo in > System Prefs > Keyboard > Shortcuts > App Shortcuts: click +, select Notes as the app, set “Pin Note” (without quotes) as the title, and set a key combo below.