To share an event, tap the event to open the detail view, then press the share button. 
You will see the following option:
- CalShare, creates a link that self-contains all event details. aCalendar can import events from this link offline, opening the link gives you event details in a web browser including ICS download option
- Text, just the event details in text format
- File, ICS file to share, e.g. via email
- File (Messenger), ICS file to share via WhatsApp, etc
- QR code, to be scanned with any good QR/Barcode scanner
When you regularly share events with the same person(s), also have a look at sharing of calendars.