A Submit an Event button can be added to the Calendar page's Tools.

Users who submit an event will see a drop-down menu. It lists each calendar category the user has View permission for. To change this list, add or remove View permissions for specific calendars. The submission form is based on the module. This means the required fields cannot be changed. Users can be required to sign in before submitting events. Or, event submission can be open to site guests.
Once an event is submitted, it must be approved. A back-end user with Publisher permissions or higher for the related calendar category can approve it. The event will not appear in the calendar until it is approved and published. Admins can modify a submission before publishing it. Residents are not notified if a submission is declined.
To enable the Submit an Event button and add Public Submissions to your site, contact Support.