When your are using a demo account,you don't influence the market by your trades but when you are trading in a live account you can influence the market with your trades?
Is this true?

That is very true, in a point, when you are trading demo you only influence yourself in the sense that you are practicing yourself how to trade and earn money (but it is virtual for sure). And when you are trading live and win, you earn money from the market, and if you lose you give your money to the market. That is actually how you are affecting the market. But you too are affected by the market, because the market conditions are the main reasons behind moving your trades in their direction.