Most shortcuts are single keys. Press c to create an event, e to open event details, t for today, r to refresh, and z to undo, while the calendar grid is focused.
Views by number or letter. 1 or d for day, 2 or w for week, 3 or m for month, 4 or x for custom, and 5 or a for agenda.
Moving around. j or n moves to the next date range, g goes to a specific date, and / puts the cursor in the search box.
Saving uses Cmd. From the event details page, Cmd+S saves the event.
Side panel. Cmd+Option+. or Cmd+Option+, opens the Tasks and Keep side panel.
Enable if needed. If single keys do nothing, open Settings and turn on keyboard shortcuts. The full set is in the table above.