The GMAT has 4 sections:
1) Analytical Writing Assessment: Write an essay in 30 minutes to demonstrate that you can identify the flaws of an argument and provide areas for improvement.
2) Integrated Reasoning: In 30 minutes tackle 12 questions that test your ability to interpret graphs, draw conclusions from tables, analyze word problems, and answer questions using multiple sources of information (e.g. emails and tables).
3) Quantitative Section: In 75 minutes, tackle 37 math-related questions that draw from Algebra, Number Properties, Geometry, Arithmetic and other math areas. Questions are classified into Problem Solving and Data Sufficiency, which is question type unique to the GMAT test.
4) Verbal Section: In 75 minutes, tackle 41 verbal-related questions that cover reading comprehension, sentence correction, and critical reasoning.
With the wealth of GMAT prep materials out there, it can be tough to find the best resources for GMAT study. I've been tutoring for the GMAT for five years, and these are the materials I've found to be the most helpful.
GMAT General Study
The best source of practice problems is The Official Guide for GMAT Review, published by GMAC. Working through the questions in this book will prepare anybody for the questions on the test. GMAC also publishes practice tests that are just like what you'll see on test day, and they are a great way to gauge your current score and get used to the CAT format. The software, GMATPrep, is available for download from mba.com. For students who need more practice problems, I recommend
The Official Guide for GMAT Quantitative Review and
The Official Guide for GMAT Verbal Review. These books offer additional practice, but the problems are not as difficult as the problems in the The Official Guide.