You can 'Star' an event to elevate its importance, causing it to be displayed more prominently by the auto-arrange feature.
Starred events will always outrank normal events, but they do still have to compete with other Starred events when auto-arrange is choosing where to display them.
See the Auto-arrange article for more info.
How to Star an event
You can star an event with the following steps:
1. Select the event (by clicking on it with the left mouse button)
2. Click on the empty star icon that appears in the top right hand corner of the event card.
You can click on the star again if you wish to 'un-star' the event.
Note: Any Starred events will be saved and shared with your timeline.