If a visit, for example, stock information for GOOG, I will be given a stock price for every point in time. How meaningful is that stock price? Is it not the actual trades occurring that are meaningful in determining what stock I can expect to buy or sell, both in terms of quantity and price?
Prices quoted are primarily the offer prices quoted by the numerous market makers on the stock exchange(s) willing to sell you the stock. There is another price which generally isn't seen on these websites, the bid prices, which are lower prices quoted by buyers and market makers willing to buy your shares from you. You wouldn't see those prices, unless you login to your trade terminal.
How meaningful are they to you depends on what you want to do buy or sell. If you want to buy then yes they are relevant. But if you want to sell, then no. And remember some websites delay market information by 15 minutes, in case of Google you might have seen that the volume is delayed by 15 minutes. So you need to consider that also while trading, but mayn't be a concern unless you are trying to buy out the company.
The information on GOOG or other sites is the average price of the stock and is indicative of the price at with the stock would be available. The actual trades happen at different values throught the day ...
So the prices are good for most purposes and if you need the exact prices, you can thne decided to log into you trading terminal and get the actual quotes
This is similar to FX quotes or any other such quotes and give you a general sense