The Friend Stream is a slim toolbar to the right of the screen which displays important happenings from your friends such as new badges 
, mottos and achievements. Liking rooms also appears on the Stream. These will only show for those online and on your friends list, so it won’t constantly spam you with unbearable amounts of useless notifications. 

You can activate this yourself by finding the bottom toolbar with your online friends and looking to the right. The “List all friends” button is the renamed “Friends” button, but the Friend Stream is the lightning bolt next to it. The picture to the left displays the welcome message. By pressing activate, you have turned on the Friend Stream. 

From these information bubbles you can also visit the same places. For a new friendship, you can click a link to invite that person to your friends. For the motto updates you can change yours from there, and for new achieved badges the link takes you to your achievements.