The PMP certification examination is a computer-based exam that is offered at testing centers worldwide. The exam is based on much of the information contained in A Guide to the Project Management Body of Knowledge (PMBOK Guide).
The questions in the PMP Exam are based on the following process groups from the PMBOK Guide: Initiating, Planning, Executing, Controlling, Closing and Professional Responsibility. So expect questions like: Which process is applied to break down the project into smaller, more manageable elements?, or: Which Tools and Techniques are part of Risk Management Planning? Some questions use project management terms that may be interchangeable with others. There will be a few questions that require you to perform simple math calculations. Or you will be required to interpret graphs or diagrams on some questions.
The number one statement to remember is that you need to answer all questions on the exam from the perspective of the PMBOK Guide, even if you feel that this question is one of those that are not 100% aligned with the standard. Asking yourself "What would the PMBOK do?" is a good place to start.
Remember that PMI is trying to present an ideal environment for project managers that might be different from your own experience. The PMBOK Guide will help you a lot here simply because it gives the right answers to all the questions that you will encounter during the exams. Or it will at least point you in the right direction. So if you really want to be prepared for your exams, read your PMBOK Guide extensively and understand the lessons here.