The new UI has evolved from the previous design, so most things are located exactly where they were before, with the one exception of the "My" menus. These now live off a new menu, accessed by clicking your avatar icon in the top right of the page.
Infrequently accessed pages, such as "my settings", now live one click deeper, but plenty of shortcuts still exists, such as on the "my home" page.
The new "bell" icon will alert you when messages from the "chess host" have been received - system messages which are generally automated or caused by a site "event".
One further important change is board size. This will now be shown at the largest size your device will support in its current orientation, so a "Max board size" must be set if you find your current preference too large.
On smaller screens, the board will scale to use as much available screen as possible whilst remaining completely in view.. (On a phone, for example.)
A larger version of the image above can be found here.
For further help, post to the help forum thread set up for this update, right here Thread 163857
If you are an internet Explorer 8 User, this is your last chance to upgrade - this browser will become unsupported.
A general UI preview can be seen in this earlier thread Thread 163722.