The exchange price of BTC to why an unstable currency? Sometimes the ride is sometimes down and what influence it? I'm curious because I often see often up and down. Then how do you all to get the BTC that much ?? I'm still a beginner and do not know anything please help...
although there are ~15million coins in circulation.. only a few thousand coins are in exchanges that would make the difference between $300-$400. or $300-$200.
so it is not like you need to sell/buy 5million-15million coins to cause movements, you only need to spend 5000 coins to move the price by an average of $20. meaning if 25,000 coins was to be bought or sold in any one day the price will move +-$100.
now the more complicated question, why people would suddenly buy or sell..
well there are many reasons.
and if you can find all of the reasons. and know which days that most positive reasons happen at any one time. you can predictably buy, knowing the price will rise to make a profit. when you sell after a rise
and if you can find all of the reasons. and know which days that most negative reasons happen at any one time. you can predictably sell, knowing the price will fall to make a profit. when you buy back more coins after a fall.
but if we all knew these reasons. we would all be able to 'get rich quick'.. so i am sorry to inform you there is no guaranteed evidence of when its best to buy and sell as most evidence of good or bad reasons may turn out to be speculation without bases/facts backing it
Thats a great explanation as to trade or not in the market.
IF lets say some companies are trying to get into bitcoin and so they will demand BTC and will buy maybe thousands, this could cause a sudden rise of value. correct?
and got stable there 
