By default on Mac and on iPad when you open the app entry will be created for you automatically. This allows you to simply open the app and start typing.
If you want to add entry to a different day you can use calendar . After you select the day entry is created and you can simply start typing.
You can use button in list view to create entry for today. This will create new entry with the daily prompt - or if the entry already exist it will insert time separator. There is shortcut for this available:
cmd - N
You can also use
cmd - shift - N to insert your daily prompt in any opened entry.