I’d like to create a calendar and share it among people, so all can add events but they cannot change other people's events. Only the owner of the event can do this.
Is it possible?
This is not currently possible with Google Calendar. You can share a calendar with someone and allow them to make changes to it or not. Making changes includes add and editing events.
To do what you want you'd need some Frankenstein's monster with a calendar for each person that they can edit and everyone else can view.
Or you'll just need to use something besides Google Calendar.
Yes, it is possible. All you have to do is go to the Settings -> Calendars -> Choose calendar or create one -> Share this calendar. In this dialog you could enter the person you would like to share calendar with and define Permission Settings. You have to choose "See all event details".
That's it.