Before you can collaborate on your business object you share it with your social network. Business objects that are shared with your social network are called Social Objects, and Social Objects have access to all kinds of social networking features, like Conversations and easy document collaboration.
You can share a business object by opening it, clicking the Social icon or link, then clicking Share in the Social panel.
One of your co-workers might have already shared the business object. If that's the case, you'll see a Join button instead of a Share button. Click it to become a member of the Social Object.
Sharing or joining a Social Object lets you participate in social activities having to do with the object. For example, you can have online Conversations with others about the object while looking at the object's details.