smoker labyrinth

I have read quite a few posts and have bumped into the "labyrinth".  I do not where to post this so I am hoping this is the right place.  My questions or interests are as follows: 

      1.          What is it?

      2.         Why do you want it?

      3.         How do you use it?

      4.         What does it gain you for you in smoking?

      5.         How do you build one?

I hope to figure out if I want one or need one for my smoking.  Thanks