Point at or click on the markers on the map. The blue marker shows your current location, the lightening markers open notices posted from mobiles and the blobs posts from computers. There's a message dropdown under the post so you can respond to the poster.
Post up notices to find people with similar interests, let people know about events and things going on locally, advertise your trade or business, sell or recycle things and much more.
Use the new Search to highlight posts containing keywords (fox, plumber, tennis etc.) in their text or to find people you know using their screen name. To search further afield pinch or splay the map to scale out.
There's a guide to using 24-7 STREET that opens from the yellow button on the navigation bar.