First make sure you have created a group. Then go to that group under the teams section of your home page. To share a planbook, make sure you are on the "Planbooks" tab. Then click the blue, "Share Your Planbook" button. Select the planbook you want to share from the dropdown menu, and then choose the sharing level. Complete the process by selecting the blue "Share It!" button below. Your page will reload and the planbook will be shared with the group.