Use my permission settings to control who has access to my calendar

With Google Calendar you can give another user access to your calendar, possibly including the ability to schedule and edit events. For example, a manager typically wants to grant calendar access to his or her administrative assistant. 

A delegated Google Calendar is simply a shared calendar with certain edit rights for the delegate.

To delegate your calendar:

1. Sign in to your calendar at http://calendar.google.com/a/your_domain.com.
2. Click Calendar settings at the top.
3. Click Calendars.
4. In the Sharing column for your calendar, click Share this calendar or Shared: Edit settings(whichever appears).
5. In the Share with specific people box, type the email address of the person to whom you want to delegate your calendar.
6. Click Add person.
7. In the drop-down box under Permission Settings, select Make changes AND manage sharing.
8. Click Save.

After you've delegated your calendar, your delegate can sign in to their calendar and manage your calendar. For example, your delegate can follow these steps to create a new event on your calendar:

1. Sign in to Calendar (the delegate's calendar).
2. Verify that the delegated calendar shows up in the My Calendars list.
3. In the drop-down list by the delegated calendar, select Create a new event on this calendar.

If a user named Carol delegates her calendar to her administrative assistant named Jim, and Jim creates an event on Carol's calendar, the event will show up on Carol's calendar as Created by: Jim for Carol.

Reference Delegate calendar access