There are three ways to view nodes within the Node Editor: simple, connected and full. See Node Editor view modes for more information on the view modes.
Changing the view mode for individual nodes
You can change the view mode for each node by clicking the 
, 
, or 
icons on the top right corner of each node.
Changing the view mode for selected nodes
Select the nodes for which you want to change the view mode and click the , , or icons on the Node Editor toolbar. Alternatively, you can select the Edit > Simple Mode (
+S), Edit > Connected Mode (+C), or Edit > Full Mode (+F) options from the Node Editor menu bar. See Node Editor menu bar for more information.
Changing the view mode for all nodes
When none of the nodes are highlighted (active) in the Node Editor, clicking the icons in the toolbar, or selecting the same options from the Node Editor Edit menu, or using the Edit menu shortcuts, affects all nodes.
You can also customize this option in the Preferences window, and your nodes are displayed in the view mode you selected the next time you create a Node Editor window. See Node Editor Preferences for more information.