How do I use the Chatter tab?

From the Chatter tab:

  1. Click your name or photo to go to your profile page.
  2. Share what you're working on.
  3. Post files or links to share with other people.
  4. View, filter, sort, and add comments to your Chatter feed.
  5. View your people, group, and record recommendations.
  6. View your company's trending topics to see the topics that are being discussed right now in Chatter.
  7. Invite people to join your Chatter network. Invited users can view profiles, post on their feed, and join groups but can't see your Salesforce data or records

For Additional Details See Force.com's: Chatter Tab Overview