Chatter Questions allows users to ask questions in their Chatter feed, in groups, and in records. Members in your users’ groups and communities can answer questions in Chatter just as they would comment on a Chatter post. The person who asked the question or the question moderator can select a best answer, which is then prominently displayed in the feed so other users can quickly find the best response to their question.
Your users can organize their information with the question title and details about their question. They can ask the question to their followers, to a group, or to a specific person, as they can with other Chatter feed items.
To enable Chatter Questions in your organization, add the Question action to the global publisher layout. If you're using a customized publisher layout in groups or on records, make sure that the Question action is added to those layouts as well.
Similar Questions, which displays similar questions when users type a question in the feed, remains in Beta for Winter '15. For information on enabling Similar Questions for your organization, contact salesforce.com.
Chatter Desktop doesn’t support Chatter Questions.