Can any one help me with required information how a newly created coin value is assigned ? and how does the rate fluctuations occur
The market decides. If people can obtain the coin easily themselves then they will mine it rather than buying it on an exchange.
But the coin needs a use, function, purpose or reason for people to have the coin.
Basic supply and demand. If people do not buy the coin at a high price then the price gets lowered to see where people might consider buying it.
Crypto coins generators realized this and tried to tweak the parameters on the coins so that rewards are high at the start, a fast rising difficulty make the coin look rare and highly sought after, in reality the coin has just been pumped ready to dump