Nifty 50 is the benchmark or index of NSE, owned and managed by IISL, founded in 1950. Index is simply an indicator which gives an overview about the happenings in stock market. Index is simply a measure and has no physical existence. The nifty 50 shrouds 13 sectors of Indian economy in one folder. Later, sectional indices came into existence like nifty bank, nifty IT, etc.
If nifty goes up and has a green indicator, it connotes that the stock price of major companies in NSE have gone up. If nifty goes down and has a red indicator, it connotes that the stock price of major companies in NSE have gone down.