There are three main sections on the GRE General Test: analytical writing, verbal reasoning, and quantitative reasoning. If you take the test before October 2006, these sections will add up to around three hours. After October 2006, the test will take about four hours.
The analytical writing section is first on the exam. You will type two short essays into the computer, and college professors working for ETS will grade them on a scale of 0-6 (in 0.5-point increments). There are two kinds of questions, and you will answer one of each: Issue Topics and Argument Topics. For the Issue Topic, you will present your opinion on one of the statements or questions provided (for the Issue Topic you will have two options). For the Argument Topic, you will read a statement of someone's opinion and analyze the reasoning of that person's argument. You will evaluate the writer's thinking and opinion rather than offering your own. You will have 30 minutes for each question (45 minutes on the Issue Topic until October 2006). You will need to organize your response, write well, and make your essays interesting for the readers, who may read hundreds of responses to these same two prompts.
The verbal reasoning section consists of one 30-minute section until October 2006, and two 40-minute sections afterwards. One of the main requirements for doing well on this section is the ability to read an unfamiliar text and understand it well. This area of the test also has questions on vocabulary and grammar.
The quantitative reasoning section -- also known as "math" -- now consists of one 45-minute section, and will be in two 40-minute sections after October 2006. In the past, the format and contents of this section have been very similar to that of the math section of the SAT.
Scores for verbal reasoning and quantitative reasoning have been on a 200-800 point scale for decades, but will soon change, most likely to a 110-150 point scale, in one-point increments.