To select a node, click on it with the mouse (you have to use scroll bars if it is not visible)
or
use the TAB or Shift-TAB keys to move to the next or previous node. A color box marks the currently selected node. You can change this color from Preferences, Colors Font and Print.
You can also select a node from one of the 8 lists. Maps and lists are synchronized, so a node selected in a list will also be the current one in the maps.