NASDAQ though called an exchange works in method called double action whereby the highest bidder buyer competes with all other buyers and the same thing happens for the sellers. NASDAQ as an exchange is not very old but has been giving good competition to the established exchange like the NYSE.

Now for NASDAQ the auction method does not work, it is like a series of dealers which are selling stocks and each dealer has some sort of inventory of stocks as well as cash. Now NASDAQ is completely automated so going by above analogy you do not visit each dealer shop instead the computer system visits the store of each dealer and checks what prices and how much shares does each dealer have to satisfy an order.

As an example I will show how a limit order works and how a market order works. Limit means that you impose a limit on the price you are willing to pay for the stock. In the market order you are willing to pay any price which is currently in the market. For example if you need to buy 1000 shares then the dealer will give 500 shares at a price you quoted but the next 500 shares you will get at a price which can be anything based on the price the dealer procures the additional shares for you.

Market makers is the term used in NASDAQ. Market maker is a person who sells and buys shares and they keep on postinmg both bid and ask prices. You can also have access to these bid offers via a system called the SOES which is Small Order Execution System

As small investors NASDAQ is the one which provides a very option for trading apart from American Stock Exchange.

If you need to trade in penny stocks then what you need is trading in OTCBB. But be careful as penny stock trading is very risky and volatile.