Enter a private passphrase. Use the same one on every device to see the same planner. Anyone with this passphrase can read your entries, so pick something only you know.
Search past days
Recurring to-dos
These are added to the checklist automatically on the weekdays you pick. Checking one off only affects that day.
This day changed on another device
was edited somewhere else since your version. Nothing has been overwritten — pick which one to keep.