The verbal section is divided up into questions on sentence completion and analogies. In the antonym questions, a word is provided, and you must select the answer that is mostly the opposite of the given word. This is a very difficult concept for some people, so it is important to become familiar with it before taking the test.
Some people have said that it is "impossible to study vocabulary", especially since the list of possible words that can appear on the test is gigantic. It does however help if you can study word roots, so that even if you don't know precisely what a word means, you can infer a general meaning from the way it is spelled. Remember, you should always answer every question, even if you have to guess. If you can make an informed guess based on the way the word is spelled, or the way it looks (good/bad, happy/angry, etc.), then you are giving yourself at least a small edge.
For GRE General Test happening after August 1st, 2011, ETS had implemented major change over in the exam's structure. Now in the verbal section of the revised GRE test, Antonyms and Analogies have been replaced by Reading comprehension. ETS believes that reading comprehension is superior to antonyms and other single-word questions as an assessment of verbal competence. More than half the revised GRE verbal section consists in paragraphs to read and questions based on those paragraphs.