I'm confused on two counts.

Firstly, is there a difference between Group Calendar and Shared Calendar?  I have seen both terms used in my research but am not sure if they really mean the same thing.....?

And secondly, all I want is to be able to sure and view Calendars with my colleagues (of which there are only 3) in Outlook 2011 for Mac.
I've just looked at Exchange Online, Exchange Server and then Office 365 but it I'm not clear about the following:

Do I have to buy Microsoft Exchange AND Office 365 or is Exchange included in 365???

Or is there any other solution for my very simple needs?

Any help much appreciated but this novice who is trying to learn fast!