The most consolidated post explains and answers the questions and raises new questions,

The clearest guide to understand what are "Witnesses". They are essential to Steem. Without them, Steem can't exist. Support them and they'll support you. This is a core principle that most Steemians haven’t thought much about and one this post hopes to solve

Here is the source for everyone to know more about the witnesses and the nodes, why witnesses and how does one witness and how a witness is created, how are they rewarded.

Original post:
https://steemit.com/witness/@teamsteem/what-are-steem-witnesses-and-why-you-should-support-them

I hope everyone commenting here needs to go through the post for better understanding on the functionality. I'm no different than you all.