How does biomass power work?

Answer 1

"Biomass power" is not a clear and unambiguous term. I'm going to assume you mean biofuels.

Basically, the principle is "if you can burn it, you can use it as a fuel" ... and fats and oils are generally flammable, regardless of whether you pump them out of the ground or squeeze them out of a seed.

The Diesel engine was originally developed to run on anything that would burn (Diesel's original intention was to use a slurry of coal powder), so it's comparatively easy to convert a Diesel engine to run on corn oil (or soybean oil, or whatever other oil you've got lying around).

With gasoline engines it's trickier, but you can use yeast to convert the sugars in ... again, pretty much anything carbohydrate based; grains are easy, but throw in some enzymes and you can use cellulose, which means just about any part of just about any plant ... to alcohol, which is a) liquid and b) pretty flammable; you can mix a little of it in with gasoline and the engine will work more or less the same. The "more or less" is a bit problematic for newer computer-controlled engines, since it's not EXACTLY the same and they may operate suboptimally unless the computer is adjusted to compensate, but that's the basic principle.