Its easy to add somebody to your Google+ Page.  Just follow these steps.

  1. Login into your Google Account.  In the top right of your screen you will see +YourName.  This takes you to you personal Google+ page.  Click this and then on the left choose pages.

  2. Choose the page you wish to add a Manager to and click "Manage This Page"

  3. On the next page, scroll down until you see the Managers box. And click "View All Managers"

  4. You will now be presented with a page showing all of your page managers. To add a new one click "Add Managers" and enter the email address of your new manager.

  5. That's it.  The new manager will receive an email asking them to become an admin of your page.