Berley ( or Burley ) and Berley Bombs are a very effective way to attract fish.
It can make the difference of coming home empty handed or with a nice feed.
Berley is used to excite fish and to draw them to your fishing area.
Otherwise they might be scattered around the place and wont find your bait.
It will also result in fish becoming more competitive and more likely to strike.
Berley should be used sparingly otherwise you might end up overfeeding the fish before they have a go at your bait.
Berley can be collected and be made from all kinds of different sources.
It can also be bough in most fishing shops.
There are different ways of using the berley.
The following Australian video shows you how to produce a Berley Trail and explains
Berley Bombs. Very informative.