What happen between 9 am to 9:15 am (market pre open)

some one plz explain what exactly happen between 9:00 am to 9:15 am (market pre opening) .
how the market take the direction with out any orders from traders .

The objective of the pre-market session is to discover the opening price.

In the first 8 minutes are the order collection period, order entry, order modification & order cancellation happen.
In the next 4 minutes are for order matching and trade confirmation.
The next 3 minutes are the buffer period for transition from Pre- open session to the normal market.

Based on all the pre-market orders, an equilibrium price is calculated. (price at which maximum quantity can be matched), this will be the opening price.