On Desktop and Web
You can move a note to the trash by right-clicking on the note from your notes list, then selecting Move to Trash on the menu that appears. If you'd like to delete the note permanently instead, hold the alt key to change the Move to Trash option to Delete permanently.
You can view trashed notes by clicking on Trash in the left most panel, under Views. To empty the trash, right click on a trashed note, then select Empty Trash on the menu that appears.
On iOS and Android
You can delete a note by long-pressing the note in the notes list until an action menu appears, then tap on the Move to Trash option.
You can also select a note, then open the right side menu by tapping on the top right menu icon. You'll find the same option to trash a note there.
To view trashed notes, tap on the top left menu icon on your notes list, then select Trash in the side menu, under Views. To empty the trash, open a trashed note, then bring up the right side menu and select the Empty Trash option.