A stock market is a platform to buy and sell stocks. The stock quotes are decided by demand and supply.
Stock markets used to be market place where a group of buyers and sellers used to gather together and express the willingness to buy/sell a stock at a willing price. Whenever the two match a deal took place.
with the advent of IT, now the stock markets have become almost paperless. Now you open a trading account with a broker, transfer the requisite amount and you can start trading in stocks from home.
A stock market or equity market is a public (a loose network of economic transactions, not a physical facility or discrete) entity for the trading of company stock (shares) and derivatives at an agreed price; these are securities listed on a stock exchange as well as those only traded privately.
The size of the world stock market was estimated at about $36.6 trillion at the start of October 2008. The total world derivatives market has been estimated at about $791 trillion face or nominal value, 11 times the size of the entire world economy. The value of the derivatives market, because it is stated in terms of notional values, cannot be directly compared to a stock or a fixed income security, which traditionally refers to an actual value. Moreover, the vast majority of derivatives 'cancel' each other out (i.e., a derivative 'bet' on an event occurring is offset by a comparable derivative 'bet' on the event not occurring). Many such relatively illiquid securities are valued as marked to model, rather than an actual market price.