Flaked maize for brewing is very similar to common or garden cornflakes, the breakfast cereal. The main difference is that they're just corn, with no added salt, sugar or anything else.
Flaked maize is often described as an adjunct. This is how brewers usually refer to fermentables other than malted barley.
Starches inside the maize must be converted to fermentable sugars before they can be used in brewing.
You can do this in the main mash where enzymes in the base malt convert the starches in the maize, along with their own.
Corn's used in some commercial lagers to lighten the beer and above all reduce the cost of the grain bill. For this reason it's got a fairly bad press with some home brewers.
However, there's a long tradition of brewing with corn in the UK, and it's a common feature in many classic bitters and ales. As well as lightening the beer, it adds a little sweetness that's distinct from that offered by malt alone.
It smells of boiled sweetcorn, not surprisingly. If you inhale deeply it starts to smell like cornflakes.
It produces a very sweet liquid, much sweeter than malt drinks I've prepared and with none of the astringency that they often have.
Overall it's fairly bland, with light cornflake flavours.
Bitters and ales, American lagers