i am pretty it works same as stocks:
For stock trading it works like this:
highest bidding and asking price are usually displayed as:
99$ / 500 and 105$ /125 which means someone willing to buy 500 at 99$ and willing to sell 125 at 105$.
Lets stay next highest asking prices lined up like this:
100 @ 106$
200 @ 110$
1000 @ 112$
If you purchase 1000 of this stock then, you will be buying
125 of them at 105$ and
100 of them at 106$
200 of them at 110$
525 of them at 112$.
You can see these lined up ask/bid quotes using more advanced trading platform.
I believe those defined as Level II or more.
Hope I am explaining right.
Except that generally if 125 are posted on the offer, you can trade up to a thousand at that price.