Making appointments in my bosses calendar

I have Outlook set up on my new MacBook and my own calendar and bosses calendar are viewable.  I am able to move things around in his diary but whenever I enter a new appointment it adds it to my diary instead.

The laptop should have been set up with all the relevant provisions so I can't work out how to make it work.  This is my first Mac so it is a learning curve.  

Thanks in advance. 

Z