How are final stock prices arrived at? 'Everybody' knows that prices are generally governed by offer &amp; demand, but I am wondering on the details of the stock exchange here.

How are stock prices (the ones which are nicely listed every day in charts) are actually computed to a specific number based on various simultaneouse bids? 

Do they change, if no transaction is actually taking place (but there are bids)?
And how are concurring bids dealt with?
Its really quite simple, the stock price you're seeing is actually the last trade that took place, the different bids are tails of the suppliers and demanders - their maximal or minimal bids

In everyday trade the simultaneous bids arr very close, and the deals are happening all the time, more or less bids in a certain direction can point out market expectations, but in a range of minutes
This applies to high volume markets, of course