v3 features a highly customizable user interface. Different parts of the app such as charts and news have been split up so you can focus on what you care about.
You can show and hide different parts of the app by using the "View" menu. (note, the View menu will only appear if the app is displayed in the dock).
If the sidebar, watchlist, or chart panes are collapsed. You will notice expansion buttons like this to bring them back.
The inspector pane that holds key metrics (Details), News, StockTwits, and Alerts can be quickly shown and hidden by clicking on the 'i" icon in the top right corner of the watchlist view.