You can create a multi-day event by marking the time directly on the timeline first.
Click on the day where the event should start, hold the mouse button, and drag across the period you want to plan. Depending on the view, you can drag left or right across the timeline, or across longer periods and months.
When you release the mouse button, the event details panel opens automatically. The selected start and end dates are already filled in for you.
You can then add the event title, choose the calendar, adjust the color, and add further details such as a description.