Sharing Calendar in Google Apps

Anyone with manager access can share a calendar to another Gmail user.  

Go Into Calendar on your Google Apps account.

Find the calendar you want to share on the left and click the 3 dots

Select Settings and sharing 

Scroll down to Share with specific people or groups
 

click Add people and Groups

Enter the email address and set the permissions that the user will have to the calendar

They will receive an invite and the calendar will appear on their account.