Using a material from a library
First create a new material in the objects list toolbox by clicking on , or select an existing material that you would like to replace by the one in the library.
Double click on the material to open the editor. Select the material node, right-click, and change its type to linked.
In the node properties pane, edit the target parameter text box. Then select a material in the libraries toolbox, then drag and drop it in the <target> box.
You can also type the target manually in the form : library_name::material_name
Click on "Apply" to save your linked material