While DaurteFarrajotaRamos's answer is correct that there is no viewer node by default, Greg Zaal's Node Wrangler addon (which comes bundled with Blender) does implement a veiwer node of sorts in the node editor.
With Node Wrangler on, when you Shift+click a node it will connect it to the Material Output node, making it visible on the object and in the preview rollout pane. It will connect surface shaders directly to the Surface output, volume shaders directly to the Volume output, and all other datatypes (colors, vectors, and values) will be sent through an emission shader plugged inot the Surface output.
View node is available for compositing node trees only, not material or texture ones. You seem to be using Blender Cycles nodes in your image, so for those there is no preview node available.
If you want to preview the created material either use the interactive preview in the 3D window by drawing a border around your object with Ctrl + B and then pressing Shift + Z or use the preview panel in the Properties Window > Material Tab > Preview