Shanet, when people put in the buy and sell orders they are saying they will not sell for less than or not buy for more than, so at the open, even tho you might bid say 10c, if there are more sellers willing to accept 9.5c then you will get them at 9.5c. It depends on the volume of bids as well as the prices. Have a look at the pre-open and do some mental arithmetic to work out how many shares the top seller will take out, then the second highest etc. This is called the matchup. You will eventually get to the point where the potential buyers and sellers have cancelled each other out and this becomes the "indicative" price. Sometimes there will be shares still left available at the indicative price and this quantity is shown also. There will only be a trade if someone is prepared to bid at least the same as the lowest seller, if not there are no trades at open.
There is a bit more to it but I will confuse myself trying to explain how they average etc. There are books available. Cheers
