You can easily create a shared event by following these steps:
Tap the + button.
On the slider select Us.
If the event is a date, toggle This is a Date on.
Select the time.
Tap the Save button in the top right-hand corner.
You will see a navy blue event or date with a pink heart in your Cupla calendar.
Assigning an event to your partner
On the slider you can also select your partner's name instead of Us. The event is then theirs rather than shared, and they get a notification asking them to accept or decline it.
If your partner declines
A declined event disappears from your partner's calendar. It stays on yours, looking exactly as it did before, and nothing marks it as declined. There is currently no way to see their answer in the app, so if you are unsure whether a date is going ahead, it is worth asking them directly.