From the drop-down list, click the appropriate status. You can also update your status from the command box. Type /available, /busy, /dnd, /brb, /away, or /offline to set your status as Available, Busy, Do not disturb, Be right back, Away, or Offline. You can also set a duration for your status when you want to change it for a specific period ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.