You can either allow all employees to see* and add company events, or you can restrict this capability down to allow only admins to see and add company events.
You can find this setting in the Calendar tab of your Company Settings:
NB: Untick the checkbox to stop staff from being able to see and add company events to your calendar. Leave it ticked it would want them to be able to see and add company events.
* While staff may be able to see company events in your calendar, this does not include any private events where employees are not invited.