Collaboration becomes most effective when a large number of people are participating. Inviting people to join your community is one of the easiest ways to start. In Pink Petro, there are a number of ways to do this:
Share something in Pink Petro by clicking "Share" in the Actions menu. If your colleague isn't already a member, they'll have the opportunity to sign up.
Invite people you work with by clicking Send Invites in the left pane of your Overview page.
I don't see the send invites on the left pane of my overview page.