How to share a outlook client calender to a office 365 user.

Hi

We use Exchange 2007 and outlook 2010 and one of the external organisations uses office 365. A office  365 user Andy  smith has shared his calendar to a user in our organisation - Basically they sent a link which says :
Andy smith has invited you to view or subscribe to a published Calendar named Calendar.
To view this Calendar, copy and paste the following address into your browser:
All looks good.

I have shared calendar between outlook client environment. But, please can you post me step by step instructions to share a John Ryan calendar to an office 365 user.
Do I need to send a link , if so how do I generate this.

Thanks
Any hep much appreciated.