Acting on the starch in the centre of the Malt, the Dextrins and Maltose will provide us with flavour and fermentable sugar.
Dextrins provide the properties of the beer we can see and taste - body, flavour, sweetness, and head-retention. Those forms of Dextrin that can be attacked by yeast are attacked only slowly and provide conditioning in the bottle or cask.
Maltose can be further broken down by enzymes in the yeast to provide "fuel". Burning this fuel will later provide, as a by-product, alcohol.