The Create Node Menu is how to create Nodes in Shader Graph. To open the Create Node Menu either right click on the workspace in the Shader Graph Window and select Create Node or press spacebar.
At the top of the Create Node Menu is a search bar. You can search for a node by typing any part of its name in the search field.
All Nodes that are available in Shader Graph are listed in the Create Node Menu categorised by their function. Any user created Sub-graphs are also available in the Create Node Menu under Sub-graph Assets.
Selecting a Node in the Create Node Menu will add it to the workspace.
A contextual Create Node Menu filters the Nodes available to show only those that use the Data Type of a selected edge. It will list every available Port on these Nodes that matches that Data Type.
You can open a contextual Create Node Menu by dragging an Edge from a Port with left mouse button and releasing it in an empty area of the workspace.