You fill this in on the full page of an item: choose More options in the card. That creates the item straight away and opens the page.
Repeat
Choose every day, working day, week, two weeks, month or year. If you later change an item from a series, you choose Only this one, This and following or All occurrences.
Reminder
You get a signal at the moment you choose. Turn on notifications in your profile, otherwise you won't get it on your device.
Attendees
Add people to an appointment. They can answer Coming, Not coming or Maybe. For an appointment where you are a guest yourself, you answer in the card.
The menu
Right-click an item for Move to tomorrow, One hour later, Duplicate, a colour and another calendar. On a phone those choices are under the three dots in the card.
You can turn on up to 24 calendars at the same time.