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Thinking means that we Research something and think about it as like, What does the Light Bulb mean? You may ask some one.

Explaining is when we burst our Knowledge about Something to others and our Thoughts. For e.g: Your Friend may say" The light bulb is a Device which gives us Light etc."

Understanding means to fully grasp the Concept of a certain Topic and being able to Explain this to others. Arguing means to dis-Agree with someone's thoughts. For eg: You may say that the Light bulb gives us heat too and all sorts of Nonsense to others.

Knowledge starts when all of these topics , Thinking,Asking,Understanding,and being able to Explain this to others. Right now you are getting Knowledge about Knowledge.