Sometimes, you want forum navigation to be present on every page of a site. This is often done as a menu of forums on the left side of each page where the current forum is highlighted. WSN includes an option for that which you can activate at Admin Panel -> Settings -> Switches -> "Left side forum tree menu". Note that this forum tree only expands the first two levels of forums, if you have third level subforums people will need to reach them the usual way.

To edit the look of the left side forum tree menu, go to Admin Panel -> Themes -> Manage Templates -> "Stylesheet". You can style .leftmenuleft to style the table column that has the menu and .leftmenuright for the column that has the page content. .forumleftmenu is a wrapper around the full menu. The menu items are an ordered list with <ul class="catmenu"> for each group of subforums (and the main group of top level forums) and <li class="catmenulinks" for each individual forum or subforum.