HI i have some questions regarding node editor

firstly, i want to know what purpose is node editor used in blender
secondly,i dont seem to understand how to use it,so if anyone can tell me how to use it
any tutorials about about node editor will be useful

The node editor is used with Blender’s Cycles render engine to create materials.

The whole node editor? It has node trees for materials, textures, and compositing.
Materials/material nodes depend on the render engine used, texture nodes can be used with Blender render, and compositing is a post-processing step so render engine doesn’t matter. You can pretty much forget about texture nodes, they’re not used much. Material nodes and compositing on the other hand, very powerful.