To invite collaborators to a Clippboard, you must first make it into a collaborative Clippboard.  To do so, mouse over the Clippboard in the menu on the left, and click the edit pencil. Choose Manage Collaboration.

Next, you can invite collaborators.  You'll first need to select a permission level. Collaborators can be View Only, or Collaborative, which means they can add their own Clipps to your Clippboard.  You can invite anyone, whether they are a current Clipparoo user or not.  Just enter a valid email address for each collaborator. (Or, if you've already collaborated with this person on another Clippboard, you can select them from your Existing Users list.)  Next, you can preview the email that will go out, and then click the button to send your invitations.

You can invite additional collaborators at any time by clicking the Invite Collaborators button at the top of the Clippboard. 

Watch a video about collaboration.