First, you must be logged in as the Admin for your book since only the Admin can create groups or assign users to groups. If you do not see Admin in the top-level toolbar, shown in the screenshot below, then you are not logged in as the Admin.
Once you are logged in as the Admin, click on Admin in the top-level toolbar. You will be brought immediately to the User/Group Permissions tab where groups are created.
To begin creating a group, click on the New Group button. Then specify information about the new group.
Once you have entered the name of the group and chosen the permissions for the group, you will need to pick which users to put into the group. To do this, click on a user’s name and then press the right arrow to move them into the group.
If you add a user to the group and wish to remove them immediately, you can click on their name and press the left arrow key.
Once you have the name of the group entered, the permissions chosen, and the users moved to the group, press the Save button to assign those permissions to each user in the group.