When you create an Event in your Calendar and if you need to move it, you have the option of moving the event to another calendar in your account or to another calendar in another account. 

If you want to move the event to a calendar not in your account, you must first make sure that calendar has been shared with you. Once that calendar has been shared with you, you will see the shared calendar show up in your list of calendars to move the event to in your Event Editor. Follow the steps in the image below: