Stix,

Its not too hard. There are usually 2 prices showing that matter.

The back price and the lay price. It will be sikilar to this

1.33 Back price
1.40 Lay Price

You could put in to gt odds of 1.39 and you would be first in the queue to get matched until someone puts a price lower. Alternatively you could take the $1.33 and it would likely get matched instantly. It could disappear if you take too long to place the bet.

You can also put in to go to Betfair SP. This means you might put in $1.39 and if it doesn't get matched it will autmatically match at a "fair" price when the race starts. That price could be $1.33, $1.35 $1.39 or even $1.10. It depends on how the prices move.

Its not hard after you start to place a few bets.