I have been meaning to do a post on the steam cycle, otherwise known as the Rankine Cycle. It's pretty simple to describe the four-step process. The complicated part is designing, maintaining, and operating the machinery that makes it happen continuously, year after year.
The water/steam cycle is the most practical and commonly used means of converting heat energy into electrical energy. The process works like this: Fuel is burned for heat. The heat vaporizes a liquid (typically very pure water), which is then expanded through a steam turbine. Lastly it is condensed at very low pressure to extract all possible thermal energy and also to re-use the pure water.