The Canvas Renderer component renders a graphical UI object contained within a Canvas.
The Canvas Renderer has no properties exposed in the inspector.
The standard UI objects available from the menu (GameObject > Create UI) all have Canvas Renderers attached wherever they are required but you many need to add this component manually for custom UI objects. Although there are no properties exposed in the inspector, a few properties and function can be accessed from scripts - see the CanvasRenderer page in the Script Reference for full details.