The Calendar is located in a Portlet on the activities dashboard
To create a new shared calendar,
1) Go to the Activities Tab > Create Event > in the Resources Tab
2) You could add an existing Resource Group or create a new Resource Group.
To create a new Resource Group, select New at the bottom of the drop down and add the employees you wish to share the calendar with.
Below is the process of creating a new Resource Group for events. Notice that you can specify the access level for each employee. In the Sharing field, you can specify who in the company can see the group when creating new calendars.